As a reader and reviewer of psychological journals myself, I often come across misinterpretations of z-scores in longitudinal studies. Z-standardization and ipsatization often lead to misinterpretations and other methodological problems in longitudinal studies and in the analysis of groups, or profiles. In multiple discussions with experts in the analysis of longitudinal data, I found that these problems are surprising even to experts in the field, and consequently, also to younger researchers.

Therefore I recently wrote an article about pitfalls of using z-standardization and ipsatization in longitudinal studies and in the analysis of groups, or profiles.This article is currently under review in the open access journal “Frontiers in Psychology”.

I believe these problems are as relevant to reviewers and authors, as to method trainers and students of Psychology.

Please see here for the complete article (open access).

While the above mentioned article focused mainly on pitfalls of z-standardization in longitudinal studies, additional problems occur when z-scores are used for interpreting differences between groups or profiles of variables. These latter issues are discussed in detail in another article, which you can find here (also open access).