Personality and IQ have traditionally been viewed as distinct domains of human functioning. However, research over the past three decades suggests that IQ is a personality trait. In an excellent book chapter in The Cambridge Handbook of Intelligence, personality neuroscientist Colin DeYoung points out that many personality traits involve cognitive processes and abilities. It's just that IQ is primarily measured with ability tests, whereas personality tests are primarily measured with questionnaires. But this is more a reflection of a lack of ingenuity on the part of psychologists than a real difference in domain of human functioning.

It's theoretically possible to measure personality traits through ability tests. For instance, agreeableness could be measured through tests of perspective taking, conscientiousness could be measured through tests of self-control, and neuroticism could be measured through measures of emotional self-regulation. Viewing IQ as a personality trait is helpful because it puts IQ in perspective. We can take a birds eye view of all the many fascinating ways we differ from one another in cognitive processing, emotion, and motivation, while seeing where IQ fits into that bigger picture.

To help us see that picture, I analyzed data from the Eugene-Springfield community sample, which consisted of 478 mostly White participants from Eugene and Springfield, Oregon. Participants ranged in age from 20 to 85 years, and spanned all levels of educational attainment. The sample consisted of 199 males and 279 females. While the sample isn't ethnically diverse, it does have a pretty good range of IQ and personality, so we can get some sense of how IQ relates to personality in the general population. The IQ test that participants took consisted of 15 multiple-choice items that measured knowledge and abstract reasoning. The personality test measured 45 dimensions of human personality.

Consistent with prior research, IQ was most strongly related to openness to experience. Out of 9 dimensions of openness to experience, 8 out of 9 were positively related to IQ: intellectual engagement, intellectual creativity, mental quickness, intellectual competence, introspection, ingenuity, intellectual depth, and imagination. Interestingly, IQ was much more strongly related to intellectual engagement and mental quickness than imagination, ingenuity, or intellectual depth, and IQ was not related to sensitivity to beauty.

Out of 45 dimensions of personality, 23 dimensions were not related to IQ. This included gregariousness, friendliness, assertiveness, poise, talkativeness, social understanding, warmth, pleasantness, empathy, cooperation, sympathy, conscientiousness, efficiency, dutifulness, purposefulness, cautiousness, rationality, perfectionism, calmness, impulse control, imperturbability, cool-headedness, and tranquility. These qualities were not directly relevant to IQ.

8 dimensions of personality outside the openness to experience domain were positively related to IQ, including organization, toughness, provocativeness, leadership, self-disclosure, emotional stability, moderation, and happiness-- although the correlations were much smaller than with intellectual engagement and mental quickness. IQ was negatively related to orderliness, morality, nurturance, tenderness, and sociability, but again, the negative correlations were much smaller than the relationships among IQ, intellectual engagement, and mental quickness.

Given this data, where does IQ fit into the personality puzzle? While this is just a single dataset, it is consistent with other studies suggesting that the most relevant personality domain is openness to experience, particularly the dimensions that reflect the ability and drive for conscious exploration of inner mental experience. This is certainly an important slice of personality, but at the same time these findings illustrate that there are many more ways we differ from each other in cognition, emotion, and motivation that are not well measured by IQ tests.

© 2014 Scott Barry Kaufman, All Rights Reserved.

image credit: istockphoto

Note: Thanks to Colin DeYoung for providing me with the Eugene-Springfield dataset. For more correlations between IQ and personality, see the supplementary data [1, 2] for the paper "From madness to genius: The openness/intellect trait domains as a paradoxical simplex", authored by Colin DeYoung, Rachael Grazioplene, and Jordan Peterson.

If you're interested in the finer details of my analysis, see below. Correlations with IQ in parentheses. * = p < .05; ** = p < .01. Note that I changed some of the IPIP AB5C facet names to better reflect the content of the items.