I am a professor at the Psychology Department of the University of Amsterdam, where I am program leader of the Psychological Methods Group. My research focuses on the conceptual analysis of psychometric concepts, the development of new psychometric techniques, and the formation of formalized psychological theory. Much of my recent work has been focused on the use of complex systems and network models in the context of psychometrics; this work is concentrated in the psychosystems project. This website collects my columns, scientific publications, and other work.