a1 Department of Psychology, Open University of the Netherlands, Heerlen, the Netherlands; Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University, the Netherlands.
a2 Department of Psychology, Open University of the Netherlands, Heerlen, the Netherlands; Division of Psychological Medicine, Institute of Psychiatry, London, United Kingdom.
a3 Association for Scientific Research in Multiple Births, Ghent, Belgium; Department of Human Genetics, University Hospital Gasthuisberg, Katholieke Universiteit Leuven, Leuven, Belgium.
a4 Association for Scientific Research in Multiple Births, Ghent, Belgium.
This article discusses findings of two recent studies conducted in collaboration with the East Flanders Prospective Twin Survey in the field of cognitive ability. The first study examined the effect of chorion type on heritability estimates of intelligence in children. The second study investigated the causes of association between child psychopathology and lower cognitive ability. Findings of these studies are discussed in the light of the current view on cognitive ability (or ‘g’) and recommendations for future research are made.