Abstract
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.