William Stern: The Relevance of His Program of 'Differential Psychology' for Contemporary Intelligence Measurement and Research.

William Stern is mostly renowned for inventing the IQ formula. However, he is also the originator of the term 'differential psychology' itself. His program of differential psychology synthesized population-based correlational studies as well as idiosyncratic approaches focusing on unique profiles of individuals. We argue that his approach still offers valuable ideas to this day; in particular, the individualistic sub-programme of Stern's differential psychology corresponds to a large extent to ipsative testing that emphasizes a profile-based analysis of individual strengths and weaknesses.