Developing the person-oriented approach: theory and methods of analysis.

The development of paradigms, or perspectives of research takes place at the level of theory, in the domain of methodology, and in the context of existing paradigms and perspectives. The development of the person-oriented approach has made considerable progress at the level of theory. In addition, the approach has found a large number of applications. Sterba and Bauer's Keynote Article has closed a gap by discussing methodological implications of the person-oriented approach. In particular, the authors have discussed whether and, if yes, how the tenets of the person-oriented approach can be tested using tools of applied statistics popular in current empirical psychological research. Continuing this discussion, this article focuses on recent developments in all three areas. First, the importance and the implications of the concept of dimensional identity are discussed. It is argued that dimensional identity needs to be established across time and individuals for comparisons to be valid, both in person-oriented and in variable-oriented research. Second, methods not covered in Sterba and Bauer's Keynote are discussed and their application is exemplified. One focus of this discussion is on configural frequency analysis, which allows researchers to make statements about particular cells or groups of cells in cross-classifications of categorical variables. Third, person-oriented research is compared to differential psychology. It is argued that the concept of dimensional identity represents the next step in the development of a psychological subdiscipline that allows one to consider that individuals differ and develop in unique ways. These differences not only manifest in means but in any parameter, including covariance structures, and they can also manifest in the differential meaningfulness of variables for the description of individuals.