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  • 1.
    Aarnio, Mikko
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Appel, Lieuwe
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Radiology.
    Fredriksson, Mats
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology. Karolinska Inst, Dept Neurosci, Stockholm, Sweden.
    Gordh, Torsten
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Wolf, Olof
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Orthopaedics.
    Sörensen, Jens
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Radiology.
    Eriksson, Måns
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Peterson, Magnus
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    Linnman, Clas
    Harvard Med Sch, Boston Childrens Hosp, Dept Anesthesiol, Boston, MA USA.
    Visualization of painful inflammation in patients with pain after traumatic ankle sprain using [(11)C]-D-deprenyl PET/CT.2017In: Scandinavian Journal of Pain, ISSN 1877-8860, E-ISSN 1877-8879, Vol. 17, no 1, p. 418-424Article in journal (Refereed)
    Abstract [en]

    BACKGROUND AND AIMS: Positron emission tomography (PET) with the radioligand [(11)C]-D-deprenyl has shown increased signal at location of pain in patients with rheumatoid arthritis and chronic whiplash injury. The binding site of [(11)C]-D-deprenyl in peripheral tissues is suggested to be mitochondrial monoamine oxidase in cells engaged in post-traumatic inflammation and tissue repair processes. The association between [(11)C]-D-deprenyl uptake and the transition from acute to chronic pain remain unknown. Further imaging studies of musculoskeletal pain at the molecular level would benefit from establishing a clinical model in a common and well-defined injury in otherwise healthy and drug-naïve subjects. The aim of this study was to investigate if [(11)C]-D-deprenyl uptake would be acutely elevated in unilateral ankle sprain and if tracer uptake would be reduced as a function of healing, and correlated with pain localizations and pain experience.

    METHODS: Eight otherwise healthy patients with unilateral ankle sprain were recruited at the emergency department. All underwent [(11)C]-D-deprenyl PET/CT in the acute phase, at one month and 6-14 months after injury.

    RESULTS: Acute [(11)C]-D-deprenyl uptake at the injury site was a factor of 10.7 (range 2.9-37.3) higher than the intact ankle. During healing, [(11)C]-D-deprenyl uptake decreased, but did not normalize until after 11 months. Patients experiencing persistent pain had prolonged [(11)C]-D-deprenyl uptake in painful locations.

    CONCLUSIONS AND IMPLICATIONS: The data provide further support that [(11)C]-D-deprenyl PET can visualize, quantify and follow processes in peripheral tissue that may relate to soft tissue injuries, inflammation and associated nociceptive signaling. Such an objective correlate would represent a progress in pain research, as well as in clinical pain diagnostics and management.

  • 2.
    Abadir, Karim M.
    et al.
    Imperial College, London.
    Larsson, Rolf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Biases of correlograms and of AR representations of stationary series2012In: Journal of Time Series Econometrics, ISSN 1941-1928, E-ISSN 1941-1928, Vol. 4, no 1Article in journal (Refereed)
    Abstract [en]

    We derive the relation between the biases of correlograms and of estimates of auto-regressive AR(k) representations of stationary series, and we illustrate it with a simple AR example. The new relation allows for k to vary with the sample size, which is a representation that can be used for most stationary processes. As a result, the biases of the estimators of such processes can now be quantified explicitly and in a unified way.

  • 3. Adami, Johanna
    et al.
    Nyrén, Olof
    Bergström, Reinhold
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Ekbom, Anders
    Engholm, Göran
    Englund, Anders
    Glimelius, Bengt
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Oncology, Radiology and Clinical Immunology.
    Smoking and the risk of leukemia, lymphoma, and multiple myeloma (Sweden)1998In: Cancer Causes and Control, ISSN 0957-5243, E-ISSN 1573-7225, Vol. 9, no 1, p. 49-56Article in journal (Refereed)
    Abstract [en]

    While several epidemiologic studies have indicated a link between smoking and the risk of developing hematolymphoproliferative cancers (chiefly leukemias, lymphomas, and multiple myelomas), in particular myeloid leukemia, the role of tobacco in the etiology of these neoplasms remains unclear. To evaluate the potential impact of tobacco use on development of leukemia, lymphoma, and multiple myeloma, we conducted a cohort study of 334,957 Swedish construction workers using prospectively collected exposure-information with complete long-term follow-up. A total of 1,322 incident neoplasms occurred during the study period, 1971-91. We found no significant association between smoking status, number of cigarettes smoked, or duration of smoking and the risk of developing leukemias, lymphomas, or multiple myeloma. There was a suggestion of a positive association between smoking and the risk of developing Hodgkin's disease, although the rate ratios were not significantly elevated, except for young current smokers. No positive dose-risk trends emerged. Our study provides no evidence that smoking bears any major relationship to the occurrence of leukemias, non-Hodgkin's lymphomas, or multiple myeloma.

  • 4.
    Adlersson, Albert
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Is eXplainable AI suitable as a hypotheses generating tool for medical research? Comparing basic pathology annotation with heat maps to find out2023Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Hypothesis testing has long been a formal and standardized process. Hypothesis generation, on the other hand, remains largely informal. This thesis assess whether eXplainable AI (XAI) can aid in the standardization of hypothesis generation through its utilization as a hypothesis generating tool for medical research. We produce XAI heat maps for a Convolutional Neural Network (CNN) trained to classify Microsatellite Instability (MSI) in colon and gastric cancer with four different XAI methods: Guided Backpropagation, VarGrad, Grad-CAM and Sobol Attribution. We then compare these heat maps with pathology annotations in order to look for differences to turn into new hypotheses. Our CNN successfully generates non-random XAI heat maps whilst achieving a validation accuracy of 85% and a validation AUC of 93% – as compared to others who achieve a AUC of 87%. Our results conclude that Guided Backpropagation and VarGrad are better at explaining high-level image features whereas Grad-CAM and Sobol Attribution are better at explaining low-level ones. This makes the two groups of XAI methods good complements to each other. Images of Microsatellite Insta- bility (MSI) with high differentiation are more difficult to analyse regardless of which XAI is used, probably due to exhibiting less regularity. Regardless of this drawback, our assessment is that XAI can be used as a useful hypotheses generating tool for research in medicine. Our results indicate that our CNN utilizes the same features as our basic pathology annotations when classifying MSI – with some additional features of basic pathology missing – features which we successfully are able to generate new hypotheses with. 

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    XAI_BachelorThesis
  • 5.
    Adriansson, Nils
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Mattsson, Ingrid
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Forecasting GDP Growth, or How Can Random Forests Improve Predictions in Economics?2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    GDP is used to measure the economic state of a country and accurate forecasts of it is therefore important. Using the Economic Tendency Survey we investigate forecasting quarterly GDP growth using the data mining technique Random Forest. Comparisons are made with a benchmark AR(1) and an ad hoc linear model built on the most important variables suggested by the Random Forest. Evaluation by forecasting shows that the Random Forest makes the most accurate forecast supporting the theory that there are benefits to using Random Forests on economic time series. 

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  • 6.
    Aggeborn Leander, Noah
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Forcasting the Daily Air Temperature in Uppsala Using Univariate Time Series2020Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This study is a comparison of forecasting methods for predicting the daily maximum air temperatures in Uppsala using real data from the Swedish Meteorological and Hydrological Institute. The methods for comparison are univariate time series approaches suitable for the data and represent both standard and more recently developed methods. Specifically, three methods are included in the thesis: neural network, ARIMA, and naïve. The dataset is split into a training set and a pseudo out of sample test set. The assessment of which method best forecast the daily temperature in Uppsala is done by comparing the accuracy of the models when doing walk forward validation on the test set. Results show that the neural network is most accurate for the used dataset for both one-step and all multi-step forecasts. Further, the only same-step forecasts from different models that have a statically significant difference are from the neural network and naïve for one- and two-step forecasts, in favor of the neural network.

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  • 7.
    Ahlberg, Ellen
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Will Svenska Akademiens Ordlista Improve Swedish Word Embeddings?2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Unsupervised word embedding methods are frequently used for natural language processing applications. However, the unsupervised methods overlook known lexical relations that can be of value to capture accurate semantic word relations. This thesis aims to explore if Swedish word embeddings can benefit from prior known linguistic information. Four knowledge graphs extracted from Svenska Akademiens ordlista (SAOL) are incorporated during the training process using the Probabilistic Word Embeddings with Laplacian Priors (PELP) model. The four implemented PELP models are compared with baseline results to evaluate the use of side information. The results suggest that various lexical relations in SAOL are of interest to generate more accurate Swedish word embeddings.

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  • 8.
    Ahlgren, Per
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Chen, Yunwei
    Chinese Acad Sci, Chengdu Lib & Informat Ctr, SERC, Chengdu 610041, Peoples R China.
    Colliander, Cristian
    Umea Univ, Inforsk, Dept Sociol, Umea, Sweden;Umea Univ, Univ Lib, Umea, Sweden.
    van Eck, Nees Jan
    Leiden Univ, Ctr Sci & Technol Studies, Leiden, Netherlands.
    Community Detection Using Citation Relations and Textual Similarities in a Large Set of PubMed Publications2019In: 17th International Conference On Scientometrics & Informetrics (ISSI2019), Vol I / [ed] Catalano, G; Daraio, C; Gregori, M; Moed, HF; Ruocco, G, INT SOC SCIENTOMETRICS & INFORMETRICS-ISSI , 2019, p. 1380-1391Conference paper (Refereed)
    Abstract [en]

    In this contribution, the effects of enhancing direct citations, with respect to publication-publication relatedness measurement, by indirect citation relations (bibliographic coupling and co-citation) and text relations on clustering accuracy are analyzed. In total, we investigate six approaches. In one of these, direct citations are enhanced by both bibliographic coupling and co-citation, whereas text relations are used to enhance direct citations in another approach. In addition to an approach based on direct citations only, we include in the study, for comparison reasons, each approach that is involved in the enhancement of direct citations. For the evaluation of the approaches, we use a methodology proposed by earlier research. However, the used evaluation criterion is based on MeSH, arguable the most sophisticated item-level classification scheme available. The results show that the co-citation approach has the worst performance, and that the direct citations approach is outperformed by the other four investigated approaches. An approach in which direct citations are enhanced by the BM25 textual relatedness measure has the best performance, followed by the approach that combines direct citations with bibliographic coupling and co-citation. The latter performs slightly better than the bibliographic coupling approach, which in turn has a better performance than the BM25 approach.

  • 9.
    Ahlgren, Per
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Chen, Yunwei
    Scientometrics & Evaluation Research Center (SERC), Chengdu Library and Information Center of Chinese Academy of Sciences, Chengdu, China.
    Colliander, Cristian
    Department of Sociology, Inforsk, Umeå University, Umeå, Sweden; University Library, Umeå University, Umeå, Sweden.
    van Eck, Nees Jan
    Centre for Science and Technology Studies, Leiden University, The Netherlands.
    Enhancing direct citations: A comparison of relatedness measures for community detection in a large set of PubMed publications2020In: Quantitative Science Studies, E-ISSN 2641-3337, Vol. 1, no 2, p. 714-729Article in journal (Refereed)
    Abstract [en]

    The effects of enhancing direct citations, with respect to publication–publication relatednessmeasurement, by indirect citation relations (bibliographic coupling, cocitation, and extendeddirect citations) and text relations on clustering solution accuracy are analyzed. Forcomparison, we include each approach that is involved in the enhancement of direct citations.In total, we investigate the relative performance of seven approaches. To evaluate theapproaches we use a methodology proposed by earlier research. However, the evaluationcriterion used is based on MeSH, one of the most sophisticated publication-level classificationschemes available. We also introduce an approach, based on interpolated accuracy values,by which overall relative clustering solution accuracy can be studied. The results show thatthe cocitation approach has the worst performance, and that the direct citations approach isoutperformed by the other five investigated approaches. The extended direct citations approachhas the best performance, followed by an approach in which direct citations are enhancedby the BM25 textual relatedness measure. An approach that combines direct citations withbibliographic coupling and cocitation performs slightly better than the bibliographic couplingapproach, which in turn has a better performance than the BM25 approach.

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  • 10.
    Ahlgren, Per
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics. Uppsala University, University Administration, Planning Division.
    Jeppsson, Tobias
    KTH Biblioteket, KTH Royal Institute of Technology, Stockholm, Sweden.
    Stenberg, Esa
    Uppsala University, University Administration, Faculty Offices.
    Berg, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    A bibliometric analysis of battery research with the BATTERY 2030+ roadmap as point of departure2022Report (Other academic)
    Abstract [en]

    In this bibliometric study, we analyze the six battery research subfields identified in the BATTERY 2030+ roadmap: Battery Interface Genome, Materials Acceleration Platform, Recyclability, Smart functionalities: Self-healing, Smart functionalities: Sensing, and Manufacturability. In addition, we analyze the entire research field related to BATTERY 2030+ as a whole, using two operationalizations. We (a) evaluate the European standing in the subfields/the BATTERY 2030+ field in comparison to the rest of the world, and (b) identify strongholds of the subfields/the BATTERY 2030+ field across Europe. For each subfield and the field as a whole, we used seed articles, i.e. articles listed in the BATTERY 2030+ roadmap or cited by such articles, in order to generate additional, similar articles located in an algorithmically obtained classification system. The output of the analysis is publication volumes, field normalized citation impact values with comparisons between country/country aggregates and between organizations, co-publishing networks between countries and organizations, and keyword co-occurrence networks. For the results related to (a), the performance of EU & associated (countries) is similar to China and the aggregate Japan-South Korea-Singapore and well below North America regarding citation impact and with respect to the field as a whole. Exceptions are, however, the subfields Battery Interface Genome and Recyclability. For the results related to (b), there is a large variability in the EU & associated organizations regarding volume in the different subfields. For citation impact, examples of high-performing EU & associated organizations are ETH Zurich and Max Planck Society for the Advancement of Science.

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  • 11.
    Ahlgren, Per
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Jeppsson, Tobias
    KTH Royal Inst Technol KTH Lib, KTH Lib, S-10044 Stockholm, Sweden..
    Stenberg, Esa
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Berg, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    BATTERY 2030+ and its Research Roadmap: A Bibliometric Analysis2023In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 16, no 21, article id e202300333Article in journal (Refereed)
    Abstract [en]

    In this bibliometric study, we analyze two of the six battery research subfields identified in the BATTERY 2030+ roadmap: Materials Acceleration Platform and Smart functionalities: Sensing. In addition, we analyze the entire research field related to BATTERY 2030+ as a whole. We (a) evaluate the European standing in the two subfields/the BATTERY 2030+ field in comparison to the rest of the world, and (b) identify strongholds of the two subfields/the BATTERY 2030+ field across Europe. For each subfield and the field as a whole, we used seed articles, i. e. articles listed in the BATTERY 2030+ roadmap or cited by such articles, in order to generate additional, similar articles located in an algorithmically obtained classification system. The output of the analysis is publication volumes, field normalized citation impact values with comparisons between country/country aggregates and between organizations, co-publishing networks between countries and organizations, and keyword co-occurrence networks.

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  • 12.
    Ahlqvist, Kerstin
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    Bjelland, Elisabeth Krefting
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    Pingel, Ronnie
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Schlager, Angela
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    Nilsson-Wikmar, Lena
    Karolinska Inst, Dept Neurobiol Care Sci & Soc, Div Physiotherapy, Huddinge, Sweden..
    Kristiansson, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    The Association of Self-Reported Generalized Joint Hypermobility with pelvic girdle pain during pregnancy: a retrospective cohort study2020In: BMC Musculoskeletal Disorders, E-ISSN 1471-2474, Vol. 21, no 1, article id 474Article in journal (Refereed)
    Abstract [en]

    Background Pelvic girdle pain (PGP) is common during pregnancy but the causes remain poorly understood. Generalized joint hypermobility (GJH) is an inherited trait, with joint mobility beyond normal limits and is assumed to be related with PGP. The aim of this project was to study the association between self-reported GJH and the presence of PGP during pregnancy. Methods In this cohort study, 4884 Swedish-speaking women were consecutively recruited at their first visit for registration in the national antenatal screening programme in Sweden. We used the five-part questionnaire (5PQ) to assess GJH and pain drawings to identify PGP. Our primary outcome was the presence of PGP during the entire pregnancy and secondary outcomes were PGP in each trimesters. We tested the associations with logistic regression analysis, and adjusted for age and ethnicity. Results In all,2455 (50.3%) women responded to both questionnaires. The prevalence of self-reported GJH was 28.7%. A higher proportion of women with GJH than women without GJH reported PGP during the entire pregnancy (47.9% vs. 41.0%), particularly in trimester 1 (31.6% vs. 22.0%). Thus, women with GJH also had higher odds of PGP during the entire pregnancy (adjusted odds ratio (aOR) 1.27: 95% CI 1.11-1.47) and in trimester 1 (aOR 1.54: 95% CI 1.20-1.96), but the associations were not statistically significant in trimester 2 (aOR 1.24: 95% CI 0.82-1.88) or trimester 3 (aOR 1.20: 95% CI 0.99-1.45). The odds of PGP in pregnancy increased with increasing numbers of positive answers to the 5PQ (pfor linear trend < 0.001) for the entire pregnancy and in trimester 1 (pfor linear trend < 0.001), but not in trimesters 2 or 3 (p = 0.13 andp = 0.06, respectively). Conclusions Compared to women with normal joint mobility, women with GJH had higher odds of reporting PGP during pregnancy and the odds increased with number of positive responses to the 5PQ. The associations were present in trimester 1 but did not reach statistical significance in trimester 2 and 3.

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    FULLTEXT01
  • 13.
    Ahlqvist, Kerstin
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    Bjelland, Elisabeth Krefting
    Department of Rehabilitation Science and Health Technology, Department of Obstetrics and Gynecology, Akershus University Hospital, Lorenskog, Norway.Oslo Metropolitan University Oslo Norway;Department of Obstetrics and Gynecology Akershus University Hospital Lorenskog Norway.
    Pingel, Ronnie
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Schlager, Angela
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    Peterson, Magnus
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    Olsson, Christina B.
    Academic Primary Healthcare Center Stockholm County Council Huddinge Sweden, Department of Neurobiology, Care Sciences and Society, Division of Physiotherapy Karolinska Institutet Huddinge Sweden.
    Nilsson‐Wikmar, Lena
    Department of Neurobiology, Care Sciences and Society, Division of Physiotherapy Karolinska Institutet Huddinge Sweden.
    Kristiansson, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Preventive Medicine.
    Generalized joint hypermobility and the risk of pregnancy‐related pelvic girdle pain: Is body mass index of importance?—A prospective cohort study2023In: Acta Obstetricia et Gynecologica Scandinavica, ISSN 0001-6349, E-ISSN 1600-0412, Vol. 102, no 10, p. 1259-1268Article in journal (Refereed)
    Abstract [en]

    Introduction: Pelvic girdle pain (PGP) affects approximately 50% of pregnant women. The mechanisms are multifactorial but not fully understood. Women with generalized joint hypermobility (GJH) may be vulnerable to load in the pelvic joints during pregnancy. Our aim was to investigate if women with GJH had an increased risk of PGP and higher pain intensity during and after pregnancy, compared with women with normal joint mobility. We also studied if body mass index (BMI) in early pregnancy influenced that risk.

    Material and methods: A prospective cohort study of 356 women, whose data were collected by self-reports and clinical examinations in early and in late pregnancy and 9 months after childbirth. GJH was present with ≥5/9 points on the Beighton score. PGP was defined by a pain drawing and ≥1 positive test. Pain intensity was measured with a visual analogue scale (0-100 mm). We adjusted for age and origin in logistic regression and ordinal logistic regression analysis.

    Results: In early pregnancy, 47.1% of the women with GJH had PGP vs 32.6% of women with normal joint mobility (adjusted odds ratio [aOR] 1.76; 95% confidence interval [CI] 0.86-3.62) and had higher odds of reporting higher pain intensity (aOR 2.04; 95% CI 1.02-4.07). The odds of PGP were highest for women with GJH and BMI ≥25 kg/m2 (aOR 6.88; 95% CI 1.34-35.27) compared with women with normal joint mobility and BMI <25 kg/m2 . The estimated associations were weaker and not statistically significant in late pregnancy or after childbirth.

    Conclusions: Women with GJH did not have an increased risk of PGP during or after pregnancy but reported higher pain intensity in early pregnancy compared with women with normal joint mobility. Since women with combined GJH and BMI ≥25 kg/m2 had the highest odds of PGP in early pregnancy, our results may suggest that health care needs to pay attention to and develop methods to reduce the risk of PGP and delay the onset of pain during pregnancy in women with this combination.Keywords: Uppsala pelvic pain study; body mass index; generalized joint hypermobility; pelvic girdle pain; pregnancy.

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  • 14.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    A homogeneity test of large dimensional covariance matrices under non-normality2018In: Kybernetika (Praha), ISSN 0023-5954, E-ISSN 1805-949X, Vol. 54, no 5, p. 908-920Article in journal (Refereed)
    Abstract [en]

    A test statistic for homogeneity of two or more covariance matrices is presented when the distributions may be non-normal and the dimension may exceed the sample size. Using the Frobenius norm of the difference of null and alternative hypotheses, the statistic is constructed as a linear combination of consistent, location-invariant, estimators of trace functions that constitute the norm. These estimators are defined as U-statistics and the corresponding theory is exploited to derive the normal limit of the statistic under a few mild assumptions as both sample size and dimension grow large. Simulations are used to assess the accuracy of the statistic.

  • 15.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    A significance test of the RV coefficient in high dimensions2019In: Computational Statistics & Data Analysis, ISSN 0167-9473, E-ISSN 1872-7352, Vol. 131, p. 116-130Article in journal (Refereed)
    Abstract [en]

    The RV coefficient is an important measure of linear dependence between two multivariate data vectors. Using unbiased and computationally efficient estimators of its components, a modification to the RV coefficient is proposed, and used to construct a test of significance for the true coefficient. The modified estimator improves the accuracy of the original and, along with the test, can be applied to data with arbitrarily large dimensions, possibly exceeding the sample size, and the underlying distribution need only have finite fourth moment. Exact and asymptotic properties are studied under fairly general conditions. The accuracy of the modified estimator and the test is shown through simulations under a variety of parameter settings. In comparisons against several existing methods, both the proposed estimator and the test exhibit similar performance to the distance correlation. Several real data applications are also provided.

  • 16.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    A unified approach to testing mean vectors with large dimensions2019In: AStA Advances in Statistical Analysis, ISSN 1863-8171, E-ISSN 1863-818X, Vol. 103, no 4, p. 593-618Article in journal (Refereed)
    Abstract [en]

    A unified testing framework is presented for large-dimensional mean vectors of one or several populations which may be non-normal with unequal covariance matrices. Beginning with one-sample case, the construction of tests, underlying assumptions and asymptotic theory, is systematically extended to multi-sample case. Tests are defined in terms of U-statistics-based consistent estimators, and their limits are derived under a few mild assumptions. Accuracy of the tests is shown through simulations. Real data applications, including a five-sample unbalanced MANOVA analysis on count data, are also given.

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  • 17.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    A U-statistic approach for a high-dimensional two-sample mean testing problem under non-normality and Behrens-Fisher setting2014In: Annals of the Institute of Statistical Mathematics, ISSN 0020-3157, E-ISSN 1572-9052, Vol. 66, no 1, p. 33-61Article in journal (Refereed)
    Abstract [en]

    A two-sample test statistic is presented for testing the equality of mean vectors when the dimension, , exceeds the sample sizes, , and the distributions are not necessarily normal. Under mild assumptions on the traces of the covariance matrices, the statistic is shown to be asymptotically Chi-square distributed when . However, the validity of the test statistic when is fixed but large, including , and when the distributions are multivariate normal, is shown as special cases. This two-sample Chi-square approximation helps us establish the validity of Box's approximation for high-dimensional and non-normal data to a two-sample setup, valid even under Behrens-Fisher setting. The limiting Chi-square distribution of the statistic is obtained using the asymptotic theory of degenerate -statistics, and using a result from classical asymptotic theory, it is further extended to an approximate normal distribution. Both independent and paired-sample cases are considered.

  • 18.
    Ahmad, M Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Generalized tests of correlation for vectors with large dimensions using modified RV coefficient2019Report (Other academic)
    Abstract [en]

    Tests of zero correlation between two or more vectors with large dimension, possibly largerthan the sample size, are considered when the data may not necessarily follow a normal distribution. A single sample case for several vectors is rst proposed, which is then extended tothe common covariance matrix under the assumption of homogeneity across several independentpopulations. The test statistics are constructed using a recently proposed modicationof the RV coecient for high-dimensional vectors. The accuracy of the tests is shown through simulations.

  • 19.
    Ahmad, M Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Location-invariant and non-invariant tests for large dimensional covariance matrices under normality and non-normality2014Report (Other academic)
    Abstract [en]

    Test statistics for homogeneity, sphericity and identity of high-dimensional covariance matrices are presented under a wide variety of very general conditions when the dimension of the vector, $p$, may exceed the sample size, $n_i$, $i = 1, \ldots, g$. First, location-invariant tests are presented under normality assumption, followed by their robustness to normality by replacing the normality assumption with a mild alternative multivariate model. The two types of tests are then presented in non-invariant form, again under normality and non-normality. Tests of homogeneity of covariance matrices in all cases are immediately supplemented by the tests for sphericity and identity of the common covariance matrix under the null hypothesis. Both location-invariant and non-invariant tests are composed of estimators that are defined as $U$-statistics with kernels of different degrees. Hence, the asymptotic theory of $U$-statistics is employed to arrive at the limiting null and alternative distributions of tests for all cases. These limit distributions are derived using a very mild and practically viable set of assumptions mainly on the traces of the unknown covariance matrices. Finally, corrections and improvements of a few other tests are also presented.

  • 20.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Location-invariant Multi-sample U-tests for Covariance Matrices with Large Dimension2017In: Scandinavian Journal of Statistics, ISSN 0303-6898, E-ISSN 1467-9469, Vol. 44, no 2, p. 500-523Article in journal (Refereed)
    Abstract [en]

    For two or more multivariate distributions with common covariance matrix, test statistics for certain special structures of the common covariance matrix are presented when the dimension of the multivariate vectors may exceed the number of such vectors. The test statistics are constructed as functions of location-invariant estimators defined as U-statistics, and the corresponding asymptotic theory is used to derive the limiting distributions of the proposed tests. The properties of the test statistics are established under mild and practical assumptions, and the same are numerically demonstrated using simulation results with small or moderate sample sizes and large dimensions.

  • 21.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Location-invariant tests of homogeneity of large-dimensional covariance matrices2017In: Journal of Statistical Theory and Practice, ISSN 1559-8608, E-ISSN 1559-8616, Vol. 11, no 4, p. 731-745Article in journal (Refereed)
    Abstract [en]

    A test statistic for homogeneity of two or more covariance matrices of large dimensions is presented when the data are multivariate normal. The statistic is location-invariant and defined as a function of U-statistics of non-degenerate kernels so that the corresponding asymptotic theory is employed to derive the limiting normal distribution of the test under a few mild and practical assumptions. Accuracy of the test is shown through simulations with different parameter settings.

  • 22.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Multiple comparisons of mean vectors with large dimension under general conditions2019In: Journal of Statistical Computation and Simulation, ISSN 0094-9655, E-ISSN 1563-5163, Vol. 89, no 6, p. 1044-1059Article in journal (Refereed)
    Abstract [en]

    Multiple comparisons for two or more mean vectors are considered when the dimension of the vectors may exceed the sample size, the design may be unbalanced, populations need not be normal, and the true covariance matrices may be unequal. Pairwise comparisons, including comparisons with a control, and their linear combinations are considered. Under fairly general conditions, the asymptotic multivariate distribution of the vector of test statistics is derived whose quantiles can be used in multiple testing. Simulations are used to show the accuracy of the tests. Real data applications are also demonstrated.

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  • 23.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics. Uppsala Univ, Dept Stat, Uppsala, Sweden.
    On Testing Sphericity and Identity of a Covariance Matrix with Large Dimensions2016In: Mathematical Methods of Statistics, ISSN 1066-5307, E-ISSN 1934-8045, Vol. 25, no 2, p. 121-132Article in journal (Refereed)
    Abstract [en]

    Tests for certain covariance structures, including sphericity, are presented when the data may be high-dimensional but not necessarily normal. The tests are formulated as functions of location-invariant estimators defined as U-statistics of higher order kernels. Under a few mild assumptions, the limit distributions of the tests are shown to be normal. The accuracy of the tests is demonstrated by simulations.

  • 24.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Testing homogeneity of several covariance matrices and multi-sample sphericity for high-dimensional data under non-normality2017In: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 46, no 8, p. 3738-3753Article in journal (Refereed)
    Abstract [en]

    A test for homogeneity of g 2 covariance matrices is presented when the dimension, p, may exceed the sample size, n(i), i = 1, ..., g, and the populations may not be normal. Under some mild assumptions on covariance matrices, the asymptotic distribution of the test is shown to be normal when n(i), p . Under the null hypothesis, the test is extended for common covariance matrix to be of a specified structure, including sphericity. Theory of U-statistics is employed in constructing the tests and deriving their limits. Simulations are used to show the accuracy of tests.

  • 25.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Tests for independence of vectors with large dimension2017Report (Other academic)
    Abstract [en]

    Given a random sample of n iid vectors, each of dimension p and partitioned into b sub- vectors of sizes pi, i = 1;:::;b. Location-invariant and non-invariant test statistics for independence of sub-vectors are presented when pi may exceed n and the distribution need not be normal. The tests are composed of U -statistics based estimators of the Frobenius norm of the di erence between the null and alternative hypotheses. Asymptotic distributions of the tests are provided for n;pi! 1, where their nite-sample performance is demonstrated through simulations. Some related and subsequent tests are brie y described. Relations of the proposed tests to certain multivariate measures are discussed, which are of interest on their own.

  • 26.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Tests for proportionality of matrices with large dimension2022In: Journal of Multivariate Analysis, ISSN 0047-259X, E-ISSN 1095-7243, Vol. 189, article id 104865Article in journal (Refereed)
    Abstract [en]

    A test for proportionality of two covariance matrices with large dimension, possibly larger than the sample size, is proposed. The test statistic is simple, computationally efficient, and can be used for a large class of multivariate distributions including normality. The properties of the statistic, including asymptotic distribution, are given under high-dimensional set up. Through simulations, the statistic is shown to perform accurately, and outperform its recent competitors, constructed on the basis of similar principles. An extension to the multi-sample case is given.

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  • 27.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Tests of Zero Correlation Using Modified RV Coefficient for High-Dimensional Vectors2019In: Journal of Statistical Theory and Practice, ISSN 1559-8608, E-ISSN 1559-8616, Vol. 13, no 3, article id 43Article in journal (Refereed)
    Abstract [en]

    Tests of zero correlation between two or more vectors with large dimension, possibly larger than the sample size, are considered when the data may not necessarily follow a normal distribution. A single-sample case for several vectors is first proposed, which is then extended to the common covariance matrix under the assumption of homogeneity across several independent populations. The test statistics are constructed using a recently proposed modification of the RV coefficient (a correlation coefficient for vector-valued random variables) for high-dimensional vectors. The accuracy of the tests is shown through simulations.

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  • 28.
    Ahmad, M. Rauf
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics. Swedish Univ Agr Sci, Dept Energy & Technol, Uppsala, Sweden.
    U-Tests of General Linear Hypotheses for High-Dimensional Data Under Nonnormality and Heteroscedasticity2015In: Journal of Statistical Theory and Practice, ISSN 1559-8608, E-ISSN 1559-8616, Vol. 9, no 3, p. 544-570Article in journal (Refereed)
    Abstract [en]

    Test statistics are presented for general linear hypotheses, with special focus on the two-sample profile analysis. The statistics are a modification to the classical Hotelling’s T2 statistic, are basically designed for the case when the dimension, p, may exceed the sample sizes, ni, and are valid under the violation of any assumption associated with T2, such as normality, homoscedasticity, or equal sample sizes. Under a few mild assumptions replacing the classical ones, the test statistics are shown to follow a normal limit under both the null and alternative hypothesis. As the test statistics are defined as a linear combination of U-statistics, the limits are correspondingly obtained using the asymptotic theory of degenerate (for null) and nondegenerate (for alternative) U-statistics. Simulation results, under a variety of parameter settings, are used to show the accuracy and robustness of the test statistics. Practical application of the tests is also illustrated using a few real data sets.

  • 29.
    Ahmad, M. Rauf
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Ahmed, S. Ejaz
    Brock Univ, Dept Math & Stat, St Catharines, ON, Canada..
    On the distribution of the T-2 statistic, used in statistical process monitoring, for high-dimensional data2021In: Statistics and Probability Letters, ISSN 0167-7152, E-ISSN 1879-2103, Vol. 168, article id 108919Article in journal (Refereed)
    Abstract [en]

    A modification to the asymptotic distribution of the T-2-statistic used in multivariate process monitoring is provided when the dimension of the vectors may exceed the sample size. Under certain mild condition, a unified limit distribution is obtained that is applicable for both Phase I and II charts. Further the limit holds for charts based on individual observations as well as subgroup means. The limit is easily applicable and does not need any data preprocessing or dimension reduction. Simulations are used to demonstrate the accuracy of the proposed limit.

  • 30.
    Ahmad, M. Rauf
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Ahmed, S. Ejaz
    Brock Univ, Dept Math & Stat, St Catharines, ON, Canada.
    Some correlation tests for vectors of large dimension2023In: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 52, no 7, p. 2144-2160Article in journal (Refereed)
    Abstract [en]

    For a random sample of n iid p-dimensional vectors, each partitioned into b sub-vectors of dimensions pi, i=1,…,b, tests for zero correlation of sub-vectors are presented when pi ≫ n and the distribution need not be normal. The test statistics are composed of U-statistics based estimators of the Frobenius norm measuring the distance between the null and alternative hypotheses. Asymptotic distributions of the tests are provided for n,pi → ∞, with their finite-sample performance demonstrated through simulations. Some related tests are discussed. A real data application is also given.

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  • 31.
    Ahmad, M. Rauf
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Pavlenko, Tatjana
    KTH, Stockholm, Sweden.
    A U-classifier for high-dimensional data under non-normality2018In: Journal of Multivariate Analysis, ISSN 0047-259X, E-ISSN 1095-7243, Vol. 167, p. 269-283Article in journal (Refereed)
    Abstract [en]

    A classifier for two or more samples is proposed when the data are high-dimensional and the distributions may be non-normal. The classifier is constructed as a linear combination of two easily computable and interpretable components, the U-component and the P-component. The U-component is a linear combination of U-statistics of bilinear forms of pairwise distinct vectors from independent samples. The P-component, the discriminant score, is a function of the projection of the U-component on the observation to be classified. Together, the two components constitute an inherently bias-adjusted classifier valid for high-dimensional data. The classifier is linear but its linearity does not rest on the assumption of homoscedasticity. Properties of the classifier and its normal limit are given under mild conditions. Misclassification errors and asymptotic properties of their empirical counterparts are discussed. Simulation results are used to show the accuracy of the proposed classifier for small or moderate sample sizes and large dimensions. Applications involving real data sets are also included.

  • 32.
    Ahmad, M. Rauf
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    von Rosen, D.
    Tests for high-dimensional covariance matrices using the theory of U-statistics2015In: Journal of Statistical Computation and Simulation, ISSN 0094-9655, E-ISSN 1563-5163, Vol. 85, no 13, p. 2619-2631Article in journal (Refereed)
    Abstract [en]

    Test statistics for sphericity and identity of the covariance matrix are presented, when the data are multivariate normal and the dimension, p, can exceed the sample size, n. Under certain mild conditions mainly on the traces of the unknown covariance matrix, and using the asymptotic theory of U-statistics, the test statistics are shown to follow an approximate normal distribution for large p, also when p >> n. The accuracy of the statistics is shown through simulation results, particularly emphasizing the case when p can be much larger than n. A real data set is used to illustrate the application of the proposed test statistics.

  • 33.
    Ahmad, M. Rauf
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Von Rosen, Dietrich
    Tests of Covariance Matrices for High Dimensional Multivariate Data Under Non Normality2015In: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 44, no 7, p. 1387-1398Article in journal (Refereed)
    Abstract [en]

    Ahmad et al. (in press) presented test statistics for sphericity and identity of the covariance matrix of a multivariate normal distribution when the dimension, p, exceeds the sample size, n. In this note, we show that their statistics are robust to normality assumption, when normality is replaced with certain mild assumptions on the traces of the covariance matrix. Under such assumptions, the test statistics are shown to follow the same asymptotic normal distribution as under normality for large p, also whenp >> n. The asymptotic normality is proved using the theory of U-statistics, and is based on very general conditions, particularly avoiding any relationship between n and p.

  • 34.
    Ahmad, M. Rauf
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    von Rosen, Dietrich
    Singull, Martin
    A note on mean testing for high dimensional multivariate data under non-normality2013In: Statistica Neerlandica, ISSN 0039-0402, E-ISSN 1467-9574, Vol. 67, no 1, p. 81-99Article in journal (Refereed)
    Abstract [en]

    A test statistic is considered for testing a hypothesis for the mean vector for multivariate data, when the dimension of the vector, p, may exceed the number of vectors, n, and the underlying distribution need not necessarily be normal. With n,p?8, and under mild assumptions, but without assuming any relationship between n and p, the statistic is shown to asymptotically follow a chi-square distribution. A by product of the paper is the approximate distribution of a quadratic form, based on the reformulation of the well-known Box's approximation, under high-dimensional set up. Using a classical limit theorem, the approximation is further extended to an asymptotic normal limit under the same high dimensional set up. The simulation results, generated under different parameter settings, are used to show the accuracy of the approximation for moderate n and large p.

  • 35.
    Ahmad, M.Rauf
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Yamada, Takayuki
    Testing homogeneity of several covariance matrices and multi-sample sphericity for high-dimensional data2013Report (Other academic)
    Abstract [en]

    A test statistic for testing homogeneity of g 2 covariance matri-ces is presented when the data are assumed multivariate normal and thedimension of the vector, p, may exceed the number of such vectors, ni,i = 1; : : : ; g. U-statistics based unbiased and location-invariant estima-tors are used to dene the test statistic. Further, using the asymptotictheory of U-statistics, the test statistic is shown to follow an approximatenormal distribution. This limiting distribution is based on certain mildassumptions on the traces of the unknown common population covariancematrix. Under the null hypothesis of homogeneity of covariance matrices,the test statistic is further extended to test multi-sample sphericity andidentity of the common covariance matrix.

  • 36.
    Ahmad, Rauf M.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Some tests for high-dimensional one-way MANOVA and related hypotheses under non-normality and heteroscedasticity2014Report (Other academic)
    Abstract [en]

    A test statistic for the equality of g 2 mean vectors, with particularemphasis on the MANOVA case for g 3, is derived when the dimensionp of the vectors may exceed the number of such vectors, ni, i = 1; : : : ; g.The asymptotic distribution of the test statistic, composed of linear com-binations of one- and two-sample U-statistics with degenerate bivariatekernels, is derived under fairly general conditions. In particular, the g pop-ulations do not need to be necessarily normal and may also have unequalcovariance matrices. Under certain mild assumptions on the moments ofthe eigenvalues of unknown covariance matrices, the limit distribution ofthe test statistic is shown to follow a 2 distribution, further extended tonormal limit, as ni; p ! 1. The statistic is further extended for testingany general linear hypothesis, taking prole analysis as one of the mostcommonly used cases. Extensive simulation results are used to show theaccuracy of the test statistic for both test size and power. Practical useof the test statistics is also demonstrated using real data examples.

  • 37.
    Ahmadi, Zainab
    et al.
    Lund Univ, Div Resp Med & Allergol, Dept Clin Sci, Lund, Sweden.
    Sundh, Josefin
    Univ Orebro, Sch Med Sci, Dept Resp Med, Orebro, Sweden.
    Bornefalk-Hermansson, Anna
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Ekström, Magnus
    Lund Univ, Div Resp Med & Allergol, Dept Clin Sci, Lund, Sweden.
    Long-Term Oxygen Therapy 24 vs 15 h/day and Mortality in Chronic Obstructive Pulmonary Disease2016In: PLOS ONE, E-ISSN 1932-6203, Vol. 11, no 9, article id e0163293Article in journal (Refereed)
    Abstract [en]

    Long-term oxygen therapy (LTOT) >= 15 h/day improves survival in hypoxemic chronic obstructive pulmonary disease ( COPD). LTOT 24 h/day is often recommended but may pose an unnecessary burden with no clear survival benefit compared with LTOT 15 h/day. The aim was to test the hypothesis that LTOT 24 h/day decreases all-cause, respiratory, and cardiovascular mortality compared to LTOT 15 h/day in hypoxemic COPD. This was a prospective, observational, population-based study of COPD patients starting LTOT between October 1, 2005 and June 30, 2009 in Sweden. Overall and cause-specific mortality was analyzed using Cox and Fine-Gray regression, controlling for age, sex, prescribed oxygen dose, PaO2 (air), PaCO2 (air), Forced Expiratory Volume in one second (FEV1), WHO performance status, body mass index, comorbidity, and oral glucocorticoids. A total of 2,249 included patients were included with a median follow-up of 1.1 years (interquartile range, 0.6-2.1). 1,129 (50%) patients died and no patient was lost to follow-up. Higher LTOT duration analyzed as a continuous variable was not associated with any change in mortality rate (hazard ratio [HR] 1.00; (95% confidence interval [CI], 0.98 to 1.02) per 1 h/day increase above 15 h/day. LTOT exactly 24 h/day was prescribed in 539 (24%) patients and LTOT 15-16 h/day in 1,231 (55%) patients. Mortality was similar between the groups for all-cause, respiratory and cardiovascular mortality. In hypoxemic COPD, LTOT 24 h/day was not associated with a survival benefit compared with treatment 15-16 h/day. A design for a registry-based randomized trial (R-RCT) is proposed.

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  • 38.
    Aho, André
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    A Statistical Analysis of Weighting Techniques for Portfolio Construction: Insights for Portfolio Managers and Investors2023Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis investigates the relative merits and drawbacks of six portfolio weighting techniques, including two traditional (equal and value-weighting), two optimization-based (mean-variance and risk parity), and two statistical (principal component analysis and ridge regression) techniques. The focus is thus on selecting the weighting technique, an aspect of portfolio construction that market practitioners sometimes overlook. The analysis, implemented on the Swedish market, employs historical backtesting, Monte Carlo simulations, and stress tests to evaluate various techniques under diverse market conditions. The results reveal that no single portfolio consistently outperforms or underperforms across all metrics and scenarios, highlighting the importance of a comprehensive set of performance and risk measures for informed investment decisions. Furthermore, the statistical techniques, principal component analysis and ridge regression demonstrate competitive risk-adjusted returns relative to the traditional and optimization-based techniques implemented in this thesis. The results suggest that market practitioners should consider incorporating these somewhat uncommon techniques alongside more traditional techniques in portfolio management, depending on their investment objectives and risk tolerance.

  • 39.
    Aho, André
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Löw, Simon
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Statistical arbitrage: Can a pairs trading strategy beat a buy-and-hold strategy?2022Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this thesis, the aim is to investigate whether a pairs trading strategy on Swedish stocks can generate a higher risk-adjusted return compared to a buy-and-hold strategy on a benchmark index. The benchmark index is the OMX Stockholm Benchmark-index (OMXSBPI), which is an index that should reflect the Swedish market in general. With a statistical focus, a trading algorithm is built which is then evaluated on data between the years 2018 to 2021. The statistical concepts this thesis is based on are stationarity and cointegration and it is the Augmented Dickey-Fuller test that forms the basis for being able to test these concepts. The risk-adjusted return for the strategy is evaluated using the popular measure Sharpe ratio, which is then compared to the Sharpe ratio for the OMXSBPI-index. The results obtained in this study can not confirm that the pairs trading strategy is better than a buy-and-hold strategy on the OMXSBPI-index in terms of risk-adjusted return. One indication, however, is that the strategy seems to perform better in conditions when the market is declining. In 2018, the index went down by 7.7060 while the strategy went up by 7.5100 percent. As it is data for only one year, it is not possible to determine whether it is due to chance or a potential edge of the strategy. 

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  • 40.
    AIDOO, ERIC
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Forecast Performance Between SARIMA and SETAR Models: An Application to Ghana Inflation Rate2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In recent years, many research works such as Tiao and Tsay (1994), Stock and Watson (1999), Chen et al. (2001), Clements and Jeremy (2001), Marcellino (2002), Laurini and Vieira (2005) and others have described the dynamic features of many macroeconomic variables as nonlinear. Using the approach of Keenan (1985) and Tsay (1989) this study shown that Ghana inflation rates from January 1980 to December 2009 follow a threshold nonlinear process.  In order to take into account the nonlinearity in the inflation rates we then apply a two regime nonlinear SETAR model to the inflation rates and then study both in-sample and out-of-sample forecast performance of this model by comparing it with the linear SARIMA model.

    Based on the in-sample forecast assessment from the linear SARIMA and the nonlinear SETAR models, the forecast measure MAE and RMSE suggest that the nonlinear SETAR model outperform the linear SARIMA model. Also using multi-step-ahead forecast method we predicted and compared the out-of-sample forecast of the linear SARIMA and the nonlinear SETAR models over the forecast horizon of 12 months during the period of 2010:1 to 2010:12. From the results as suggested by MAE and RMSE, the forecast performance of the nonlinear SETAR models is superior to that of the linear SARIMA model in forecasting Ghana inflation rates.

    Thought the nonlinear SETAR model is superior to the SARIMA model according to MAE and RMSE measure but using Diebold-Mariano test, we found no significant difference in their forecast accuracy for both in-sample and out-of-sample.

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  • 41.
    Akrami, Nazar
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Ekehammar, Bo
    Yang-Wallentin, Fan
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Personality and Social Psychology Factors Explaining Sexism2011In: Journal of Individual Differences, ISSN 1614-0001, E-ISSN 2151-2299, Vol. 32, no 3, p. 153-160Article in journal (Refereed)
    Abstract [en]

    Previous research has almost exclusively examined sexism (negative attitudes toward women) from either a personality or a social-psychology perspective. In two studies (N = 379 and 182, respectively), we combine these perspectives and examine whether sexism is best explained by personality (Big-Five factors, social dominance orientation, and right-wing authoritarianism) or by social-psychological (group membership and group identification) variables - or by a combination of both approaches. Causal modeling and multiple regression analyses showed that, with the present set of variables, sexism was best explained by considering the combined influence of both personality- and social-psychology constructs. The findings imply that it is necessary to integrate various approaches to explain prejudice.

  • 42.
    Al-Adili, Lina
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Food Studies, Nutrition and Dietetics.
    Boström, Anne‐Marie
    Department of Neurobiology, Care Science and Society Division of Nursing, Karolinska Institutet Huddinge Sweden;Theme Inflammation and Aging Karolinska University Hospital Huddinge Sweden;Research and Development Unit Stockholms Sjukhem Stockholm Sweden;Karolinska Institutet Huddinge Sweden.
    Orrevall, Ylva
    Department of Biosciences and Nutrition Karolinska Institute Stockholm Sweden;Medical Unit Clinical Nutrition Women's Health and Allied Health Professionals Theme, Karolinska University Hospital Stockholm Sweden.
    Lang, Nanna R.
    Department of Nutrition and Health VIA University College Denmark.
    Peersen, Charlotte
    Department of Unit for Service and Intern Control Department of Service and Quality, Trondheim Municipality Trondheim Norway.
    Persson, Inger
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Thoresen, Lene
    Cancer Clinic, St. Olavs Hospital Trondheim University Hospital Trondheim Norway.
    Lövestam, Elin
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Food Studies, Nutrition and Dietetics.
    Self‐reported documentation of goals and outcomes of nutrition care: A cross‐sectional survey study of Scandinavian dietitians2023In: Scandinavian Journal of Caring Sciences, ISSN 0283-9318, E-ISSN 1471-6712, Vol. 37, no 2, p. 472-485Article in journal (Refereed)
    Abstract [en]

    Background

    The documentation of goals and outcomes of nutrition care in Electronic Health Records is insufficient making further exploration of this of particular interest. Identifying common features in documentation practice among Scandinavian dietitians might provide information that can support improvement in this area.

    Aims

    To explore the associations between clinical dietitians' self-reported documentation of patients' goals and outcomes and demographic factors, self-reported implementation of the systematic framework the Nutrition Care Process 4th step (NCP) and its associated terminology, and factors associated with the workplace.

    Methods

    Data from a cross-sectional study based on a previously tested web-based survey (INIS) disseminated in 2017 to dietitians in Scandinavia (n = 494) was used. Respondents were recruited through e-mail lists, e-newsletters and social media groups for dietitians. Associations between countries regarding the reported documentation of goals and outcomes, implementation levels of the NCP 4th step, demographic information and factors associated with the workplace were measured through Chi-square test. Associations between dependent- and independent variables were measured through logistic regression analysis.

    Results

    Clinically practicing dietitians (n = 347) working in Scandinavia, Sweden (n = 249), Norway (n = 60), Denmark (n = 38), who had completed dietetic education participated. The reported documentation of goals and outcomes from nutrition intervention was highly associated with the reported implementation of NCP 4th step terminology (OR = 5.26; p = 0.009, OR = 3.56; p = 0.003), support from the workplace (OR = 4.0, p < 0.001, OR = 8.89, p < 0.001) and area of practice (OR = 2.02, p = 0.017). Years since completed dietetic training and educational level did not have any significant associations with documentation practice regarding goals and outcomes.

    Conclusion

    Findings highlight strong associations between the implementation of the NCP 4th step terminology and the documentation of goals and outcomes. Strategies to support dietitians in using standardized terminology and the development of tools for comprehensive documentation of evaluation of goals and outcome are required.

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  • 43.
    Ali, Mohammad
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Performance of Three Classification Techniques in Classifying Credit Applications Into Good Loans and Bad Loans: A Comparison2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The use of statistical classification techniques in classifying loan applications into good loans and bad loans gained importance with the exponential increase in the demand for credit. It is paramount to use a classification technique with a high predictive capacity to ensure the profitability of the business venture.

     

    In this study we aim to compare the predictive capability of three classification techniques: 1) Logistic regression, 2) CART, and 3) random forests. We apply these techniques on German credit data using an 80:20 learning:test split, and compare the performance of the models fitted using the three classification techniques. The probability of default pi for each observation in the test set is calculated using the models fitted on the training dataset. Each test set sample xi is then classified into a good loan or a bad loan, based on a threshold , such that xi bad loan class if pi  . We chose several  thresholds in order to compare the performance of each of the three classification techniques on five model suitability statistics: Accuracy, precision, negative predictive value, recall, and specificity.

     

    None of the classifiers turned out to be best at all the five cross-validation statistics. However, logistic regression has the best performance at low probability of default thresholds. On the other hand, for higher thresholds, CART performs best in accuracy, precision, and specificity measures, while random forest performs best for negative predictive value and recall measures. 

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  • 44.
    Amartey, Philomina
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    A COMPARISON OF SOME ESTIMATION METHODS FOR HANDLING OMITTED VARIABLES : A SIMULATION STUDY2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Omitted variable problem is a primary statistical challenge in various observational studies. Failure to control for the omitted variable bias in any regression analysis can alter the efficiency of results obtained. The purpose of this study is to compare the performance of four estimation methods (Proxy variable, Instrumental Variable, Fixed Effect, First Difference) in controlling the omitted variable problem when they are varying with time, constant over time and slightly varying with time. Results from the Monte Carlo study showed that, the prefect proxy variable estimator performed better  than the other models under all three cases. The instrument Variable estimator performed better than the Fixed Effect and First Difference estimator except in the case when the omitted variable is constant over time. Also, the Fixed Effect performed better than First Difference estimator when the omitted variable is time-invariant and vice versa when the omitted is slightly varying with time.

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  • 45.
    Anasthase, David
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Da Souza, Camila
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Comparing ARIMA and Holt-Winters: forecasting inflation for the largest economies in the EU2020Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Forecasting inflation and other economic variables is essential for monetary policy analysis and decision making. In the following thesis the two well-known statistical methods Box-Jenkins, with its ARIMA models, and Holt-Winters are compared with each other by forecasting accuracy from predicting the month-on-month inflation rate for the ten largest economies in the European Union. Their forecasting accuracy is further compared to the accuracy provided by a random walk. From the ambiguous results, given the models specified, it cannot be concluded that a specific method is more accurate in forecasting inflation rates than the other. 

  • 46.
    Ander, Malin
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Clinical Psychology in Healthcare.
    Grönqvist, Helena
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Clinical Psychology in Healthcare.
    Cernvall, Martin
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Clinical Psychology in Healthcare.
    Engvall, Gunn
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Women's and Children's Health, Pediatrics.
    Hedström, Mariann
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Caring Sciences.
    Ljungman, Gustaf
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Women's and Children's Health, Pediatrics.
    Lyhagen, Johan
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Mattsson, Elisabet
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Clinical Psychology in Healthcare.
    von Essen, Louise
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Clinical Psychology in Healthcare.
    Development of health-related quality of life and symptoms of anxiety and depression among persons diagnosed with cancer during adolescence: a 10-year follow-up study2016In: Psycho-Oncology, ISSN 1057-9249, E-ISSN 1099-1611, Vol. 25, no 5, p. 582-589Article in journal (Refereed)
    Abstract [en]

    Objective: The main aim was to investigate the development of health-related quality of life (HRQOL) and symptoms of anxiety and depression in a cohort diagnosed with cancer during adolescence from shortly after up to 10 years after diagnosis.

    Methods: Participants (n = 61) completed the SF-36 and the HADS shortly; six, 12, and 18 months; and two, three, four, and 10 years (n = 28) after diagnosis. Polynomial change trajectories were used to model development.

    Results: Polynomial change trajectories showed an initial increase which abated over time into a decrease which abated over time for the SF-36 subscales Mental Health and Vitality; an initial decline which abated over time into an increase for HADS anxiety; and an initial decline which abated over time into an increase which abated over time for HADS depression. The SF-36 mental component summary showed no change from two to 10 years after diagnosis whereas the SF-36 physical component summary showed an increase from two years after diagnosis which declined over time. Ten years after diagnosis 29% reported possible anxiety.

    Conclusions: Development of HRQOL and symptoms of anxiety and depression appears to be nonlinear among persons diagnosed with cancer during adolescence. Well into permanent survivorship an increase in symptoms of anxiety is shown and approximately a third of the participants report possible anxiety. The findings indicate the need for: studies designed to pinpoint the times of highest psychological risk, clinical follow-up focusing on psychological problems, and development of effective psychological interventions for survivors of adolescent cancer

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  • 47.
    Andersson, Björn
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    An Evaluation of Hypothesis Testing Methods for Equating Differences in Kernel EquatingManuscript (preprint) (Other academic)
    Abstract [en]

    In observed-score equating, hypothesis tests of equating differences are helpful in deciding which equating function is suitable. Here, a hypothesis testing procedure for item response theory (IRT) observed-score kernel equating using a Wald test is introduced. Simulations evaluating the Wald test when using IRT and log-linear models are conducted. The test with either IRT or log-linear models is shown to have high power and greatly outperform the Hommel multiple hypothesis testing method. The Wald test is applied to two datasets in both an equivalent groups design and a non-equivalent groups design, showing that the Wald test can provide different conclusions to other hypothesis testing methods in practice.

  • 48.
    Andersson, Björn
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Contributions to Kernel Equating2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The statistical practice of equating is needed when scores on different versions of the same standardized test are to be compared. This thesis constitutes four contributions to the observed-score equating framework kernel equating.

    Paper I introduces the open source R package kequate which enables the equating of observed scores using the kernel method of test equating in all common equating designs. The package is designed for ease of use and integrates well with other packages. The equating methods non-equivalent groups with covariates and item response theory observed-score kernel equating are currently not available in any other software package.

    In paper II an alternative bandwidth selection method for the kernel method of test equating is proposed. The new method is designed for usage with non-smooth data such as when using the observed data directly, without pre-smoothing. In previously used bandwidth selection methods, the variability from the bandwidth selection was disregarded when calculating the asymptotic standard errors. Here, the bandwidth selection is accounted for and updated asymptotic standard error derivations are provided.

    Item response theory observed-score kernel equating for the non-equivalent groups with anchor test design is introduced in paper III. Multivariate observed-score kernel equating functions are defined and their asymptotic covariance matrices are derived. An empirical example in the form of a standardized achievement test is used and the item response theory methods are compared to previously used log-linear methods.

    In paper IV, Wald tests for equating differences in item response theory observed-score kernel equating are conducted using the results from paper III. Simulations are performed to evaluate the empirical significance level and power under different settings, showing that the Wald test is more powerful than the Hommel multiple hypothesis testing method. Data from a psychometric licensure test and a standardized achievement test are used to exemplify the hypothesis testing procedure. The results show that using the Wald test can provide different conclusions to using the Hommel procedure.

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  • 49.
    Andersson, Björn
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics.
    Bränberg, Kenny
    Department of Statistics, USBE, Umeå University.
    Wiberg, Marie
    Department of Statistics, USBE, Umeå University.
    Performing the Kernel Method of Test Equating with the Package kequate2013In: Journal of Statistical Software, E-ISSN 1548-7660, Vol. 55, no 6, p. 1-25Article in journal (Refereed)
    Abstract [en]

    In standardized testing it is important to equate tests in order to ensure that the test takers, regardless of the test version given, obtain a fair test. Recently, the kernel method of test equating, which is a conjoint framework of test equating, has gained popularity. The kernel method of test equating includes five steps: (1) pre-smoothing, (2) estimation of the score probabilities, (3) continuization, (4) equating, and (5) computing the standard error of equating and the standard error of equating difference. Here, an implementation has been made for six different equating designs: equivalent groups, single group, counterbalanced, non-equivalent groups with anchor test using either chain equating or post-stratification equating, and non-equivalent groups using covariates. An R package for the kernel method of test equating called kequate is presented. Included in the package are also diagnostic tools aiding in the search for a proper log-linear model in the pre-smoothing step for use in conjunction with the R function glm.

  • 50.
    Andersson, Björn
    et al.
    Univ Oslo, Ctr Educ Measurement, CEMO, POB 1161 Forskningspk, N-0318 Oslo, Norway..
    Jin, Shaobo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Statistics. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Statistics, AI and Data Science.
    Zhang, Maoxin
    Univ Oslo, Ctr Educ Measurement, CEMO, POB 1161 Forskningspk, N-0318 Oslo, Norway..
    Fast estimation of multiple group generalized linear latent variable models for categorical observed variables2023In: Computational Statistics & Data Analysis, ISSN 0167-9473, E-ISSN 1872-7352, Vol. 182, article id 107710Article in journal (Refereed)
    Abstract [en]

    A computationally efficient method for marginal maximum likelihood estimation of multiple group generalized linear latent variable models for categorical data is introduced. The approach utilizes second-order Laplace approximations of the integrals in the likelihood function. It is demonstrated how second-order Laplace approximations can be utilized highly efficiently for generalized linear latent variable models by considering symmetries that exist for many types of model structures. In a simulation with binary observed variables and four correlated latent variables in four groups, the method has similar bias and mean squared error compared to adaptive Gauss-Hermite quadrature with five quadrature points while substantially improving computational efficiency. An empirical example from a large-scale educational assessment illustrates the accuracy and computational efficiency of the method when compared against adaptive Gauss-Hermite quadrature with three, five, and 13 quadrature points.

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