Testing the differentiation of personality by intelligence hypothesis

Similar to the findings that variability in intelligence (IQ) test scores is higher for individuals higher in IQ, the differentiation hypothesis by Brand, Egan, and Deary (1994) is that individuals higher in IQ will also have greater variability in personality scale scores. Adult individuals (381 women and 135 men) completed a group administered IQ test and a personality scale measuring 20 traits. A median split on IQ created low and high IQ groups. For most of the personality scales and resulting factor scores, the results suggest that the higher IQ group has higher variability in scale scores, lending some support to the differentiation hypothesis of personality.