Donnerstag, 28. November 2019, 15:00 - 16:30 iCal

Talk of Dr. Dylan Molenaar|University of Amsterdam

Are Cognitive Abilities Differentiated across the Intellect?

An Item Level Approach to test for Spearman’s Law of Diminishing Returns

Faculty of Psychology, Lecture hall G, 2nd floor (left wing of the building)
Liebigasse 5, 1010 Wien


In 1927, Spearman observed that for a sample of healthy children, the correlations among intelligence test scores were smaller as compared to a sample of children with learning disabilities. On the basis of this observation, Spearman hypothesized that the structure of cognitive abilities changes across general intelligence. He furthermore hypothesized that the structure of cognitive abilities changes over the life span. Many studies into this phenomenon of cognitive ability differentiation have been conducted ever since. Typically, these studies focused on differences in the covariance structure of intelligence subtest data across groups that differ in age or general intelligence. Results have however been rather mixed showing different effects between studies or even within studies. An important aspect about these mixed results is that the differentiation effect is in essence an interaction effect which makes it challenging to study. That is, as interaction effects are scale dependent (e.g., Loftus, 1978), differentiation effects may show up differently in different subtests due to arbitrary properties of the data (e.g., difficulty of the items, number of the items, scale of the items). A possible solution to this problem is to consider the differentiation effect at the item level instead of the subtest level. Such item level analyses take the characteristics of the items into account such that the results do not depend on arbitrary properties of the data. In the present talk, a possible item level approach to test for ability differentiation is derived. The new approach is applied to the item level data of the Hungarian standardization data of the WAIS-IV to draw a conclusion on the presence of cognitive ability differentiation in these data.



Loftus, G. R. (1978). On interpretation of interactions. Memory & Cognition, 6(3), 312-319.

Spearman, C. E. (1927). The abilities of man: Their nature and measurement. New York:




Department of Applied Psychology: Health, Development, Enhancement and Intervention (Differential Psychology and Psychological Assessment)


Abla Marie-Jose Bedi
Department of Basic Psychological Research and Research Methods