I am a PhD-student and lecturer at the Psychological Methods group of the University of Amsterdam. In May 2007 I received an NWO-Toptalent grant (180.000 euro) for the project "Statistical modeling of (cognitive) ability differentiation". I will work on this project till September 2012.

A well established empirical finding is that all subtests of a multivariate intelligence test (for instance the WAIS, WISC, or K-ABC) are positively correlated although they concern distinct cognitive abilities. This phenomenon, referred to by 'the positive manifold', is explained by positing a higher order factor that is supposed to underly all cognitive abilities. This factor is called 'the general intelligence factor'. 

Past research has focused on 'the ability differentiation hypothesis'. This hypothesis states that the magnitude of the positive subtest correlations is not uniform across the range of the general intelligence factor. This research has not come with an unambiguous answer, as empirical results are quite mixed. These mixed results are possibly explained by the absence of suitable statistical procedures to investigate ability differentiation. The aim of this project is to develop, test, and apply suitable statistical models to investigate ability differentiation.