Psychological treatments tend to be created based on group averaged results of how variables relate to each other. This means that treatments may not be applicable to individual people where variables may relate to each other in other ways than seen in the group models. While the personalization of psychological treatments is on the rise, such attempts need to be accompanied by idiographic research methods in order to achieve a high degree of personalization. Ideally, treatments can be formed targeting individual specific psychological processes of change. If personalization is conducted on the basis of subgroups, such subgrouping needs to be done using idiographic methods rather than using categories defined in nomothetic research.