T HE PSYCHOLOGY OF ABILITY is a branch of psychology that examines how and why people differ from one another - as opposed to other areas of the discipline which regard such 'individual differences' as nuisances, to be ignored (or controlled for statistically) in psychology experiments. For example, social psychology studies variables that influence prejudice in the population, and does not trouble to consider whether or why some individuals are more prejudiced against minority groups than others. Cognitive psychologists try to draw inferences about neural mechanisms by studying how various features of stimuli influence response time; they are rarely interested in whether or why some individuals perform more quickly or slowly than the norm in all experimental conditions. Thus Cronbach (1957) identified two distinct disciplines of psychology. One comprises areas such as social, developmental, cognitive, physiological and behavioural psychology - branches that try to understand the broad laws that govern how people in general behave under various conditions. The second branch is that of individual differences, clinical and (some) occupational psychology, which focuses on how and why people differ from one another. And whilst there have been moves to reconcile these two approaches through experimental designs that consider both types of experimental treatment and individual differences, such studies still remain the exception rather than the rule.