Personality and Intelligence

The measurement and interpretation of intelligence has been an object of controversy since 1905. In this year Alfred Binet published his test for screening children in whose education the French government intended to invest more effort. Perhaps the greatest debate among scholars is about the relevance of computing a general intelligence score and reporting it in IQ scale points (Telzrow, 1988). This debate has started long ago and is still raging because of three reasons: 1) the attractiveness of the IQ metric for reporting and comparing, 2) the IQ metric’s popularity among the general public, and 3) the abuse of the IQ topic by some authors of popular books who lack the necessary education in psychology. The good news is that intelligence tests are refocusing to measure sets of specific cognitive abilities (Naglieri, 1988), and the goal is to interpret respondents’ profiles in terms of mismatches between the scores of these abilities (Kaufman, 1988). General intelligence, however, is worthwhile measuring as it is a reliable and very good predictor of job performance (Schmidt & Hunter, 1998), especially in more complex jobs (Hunter, 1986), and, in general, of economic well-being, personal, and professional accomplishment (Gottfredson, 1997).

Now let us define general intelligence or g, as it is alternatively called. Mackintosh (2011) defined it psychometrically as the component variance common to and discoverable in all tests of cognitive ability, whereas Wechsler (1944) defined it functionally as the global capacity of individuals to act purposefully, think rationally and to deal effectively with the environment. Both definitions are quite good for different reasons which I discuss below.

The first definition stresses on the fact that intelligence tests measure only the cognitive abilities measured in their subtests (i.e., various tasks we are asked to complete). Therefore, when someone tells you they have an IQ of 115 points, please ask them what the test they took was and what tasks they were asked to accomplish. Because it could have been a test based on, say, verbal reasoning (e.g., fox is to rabbit as lion to ____) and spatial reasoning (“A cube is rotated on its sides. From the following four rotations, which one is not an impossible rotation of this cube?”). However, exploring just two cognitive abilities is not enough to claim that we have covered the whole space of general intelligence and we cannot confidently report results in IQ points. What about your performance on working memory, perceptual speed, and other secondary (i.e., hierarchically below g) cognitive abilities as outlined in the majorly popular nowadays Cattell-Horn-Carroll (CHC; Carroll, 1993; graphic below for more information) theory of intelligence?

The second definition belonging to David Wechsler is much wiser in terms of practicality and has significance for personality research. Why? Because if intelligence is to act purposefully and intelligently deal with the environment’s challenges, the potential for personality moderating cognitive abilities comes into play. How successfully we solve environmental challenges is determined also by our personality in terms of traits, motivations, and beliefs. For example, imagine a manager who has an IQ of 130 and very high conscientiousness, and very high neuroticism. Do you think this person will fully act up to Wechsler’s definition if they have to quickly solve a critical operational problem? This manager might be very intelligent, but their neuroticism might either slow them down deciding or provoke them into making a rash decision.

The debate whether personality and intelligence are related is an old one, the notable proponents of such relationship being Cattell (1971) and Ackerman (1999). Ackerman and Heggestad’s (1997) meta-analysis found that g is significantly related to Extraversion (0.08), Neuroticism (-0.15), and Openness to experience (0.33). Except for Openness to experience, whose Intellect and Openness to Ideas facets basically assess self-reported intelligence, these correlations are quite modest. They are, however, population-corrected averages from correlations across different studies and samples of participants, and they do not help us explain the ontogenesis of the personality-intelligence interface.

A step in this direction was Brand, Egan and Deary’s (1994) hypothesis that the dimensionality of personality might be different for individuals with low and high levels of intelligence. The authors based this assumption on adults and children’s data from applications of the Eysenck’s two-factor (Extroversion – Neuroticism) personality model. Perhaps, at higher levels of g and because of g’s positive influences throughout our lives, personality becomes the more predictive factor of behavior. That is, personality becomes richer and differentiated in many ways (interests, values, motivations, etc.) with the course of our cognitive development (Brand et al., 1994). For example, we need to look at the undifferentiated personality of children (only Extraversion and Neuroticism are reliably detectable at the age of 8) and compare it with the fact that most studies on the FFM personality are done with college students of the ages 19-23, after they have cognitively (at least in terms of fluid intelligence) “maxed” at the ages of 16-18. There is recent empirical support for this so-called differentiation hypothesis (Allik & Realo, 1997; Austin et al., 2000; Harris et al., 2005). But now, let us finally satisfy our curious reader and dive deep into each FFM factor’s relationship to g.

Neuroticism. Considering the relationship between g and Neuroticism, it is notable that test anxiety relates to g as high as Openness to experience, but negatively (-0.33; Ackerman & Heggestad, 1997). Test anxiety, worrying and tension interfere with memory and attention and decrease cognitive performance (Chamorro-Premuzic & Furnham, 2005). Mohan and Kumar (1974) suggested that this is partially due to the test as well because performance of neurotics on intelligence tests deteriorated with increasing the test difficulty. Although state and trait anxiety (i.e., being anxious only momentarily and being anxious in general) are distinct psychological constructs, in the neurotic individuals they will be highly related and deteriorate intellectual performance (Humbree, 1988; Zeidner, 1995).

Extraversion. The very modest correlation of g with Extraversion varies from positive to negative (Chamorro-Premuzic & Furnham, 2005). It might be that arousing circumstances, such as when being a job applicant and taking a timed and relatively short intelligence test that will be used to determine your employment future, will favor extroverts who actively seek arousal (Eysenck, 1991). However, Moutafi, Furnham and Crump (2003) found that not extroverts but rather introverts scored higher on the Watson-Glaser intelligence test. Multiple regressions performed with the NEO-PI-R facets showed that whereas the Gregariousness and Assertiveness facets of Extraversion related negatively to g, the Activity facet related positively. Also, Wolf and Ackerman (2005) found that with older participants the positive relationship between Extraversion and intelligence turns negative, giving credence to the argument that perhaps people who develop cognitively rather early are more confident and proactive at school, peak, and after this point become more introverted.

Openness to experience. It has been argued that the last factor added to the FFM model – Openness to Experience - should be interpreted more as ability than an aspect of personality (McCrae, 1994; John & Srivastava, 1999). Chamorro-Premuzic and Furnham (2005) provide argumentation for Openness to Experience being an indirect, self-report measure of intelligence. Additionally, Brand (1994) found that g explains approximately 40% of the variance in Openness to Experience. Depending on the FFM personality test used the sizeable relationship between the two constructs can further rise. For example, in the NEO suite of personality tests being intellectual and quickly generating ideas is only covered by one of the six Openness to Experience facets – Ideas. That is why, McCrae and Costa (1997) argued that their Openness to Experience factor measures much more than just g – need for variety, appreciation for culture and art, imagination, knowledge of one’s moods, and tolerance for ambiguity. Therefore, the relationship between general intelligence and Openness to Experience might vary in relation to how this factor was made of the respective personality inventory.

Conscientiousness. Furnham et al. (2007) found that conscientious individuals tended to score lower on measures of intelligence, but the effects sizes were close to zero and with inconsistent direction. With regards to g, only the Order facet of the NEO-PI-R related negatively (-0.19). Moutafi et al. (2005) also found other negative correlations between Conscientiousness and general intelligence. The authors provided a plausible explanation – perhaps less cognitively able individuals will compensate in competitive educational and work environments by developing and increasing their Conscientiousness. Conversely, the more able by birth (i.e., the ones having higher fluid intelligence which is not the acquired through schooling crystallized intelligence) will not be very conscientious because they can rely on their superior intellect (Furnham, 2002). Support for this argument comes from the consistent negative correlation of Conscientiousness and the more biological and adaptive fluid intelligence (Moutafi et al. 2005). That is, individuals high in fluid intelligence would not need to be organized and hard-working to accomplish some work that otherwise would require high Conscientiousness.

Agreeableness. Agreeableness seem to modestly and non-significantly relate to intelligence (Ackerman & Heggestad, 1997). However, when the personality test is consequential as it is in selection for job contexts, more intelligent applicants might be able to identify the items measuring Agreeableness. As you might have correctly guessed, these intelligent applicants might report they are really kind, altruistic, and cooperative, even if that is not the truth. Chamorro-Premuzic and Furnham (2005) also suggest that because people are to some extent able to judge their intellectual abilities, highly intelligent people would have lower scores on the Modesty facet of Agreeableness. Stankov and Crawford (1996) have previously argued that Modesty relates to low self-confidence, which is a negative predictor of performance on cognitive tests as well.

All these findings are fascinating and truly confusing, that is what our reader might be already ready to tell us. Indeed, they are I will chime in. Personality is inextricably entwined with the context one is in. This context consists of complex stimuli and challenges, and we have to apply different cognitive abilities to a different degree. For example, if you see a very interesting item in a grocery store, you are at the mercy of your working memory to remember its price once you have seen 15 more interesting items. However, at the cashiers you are also at the mercy of your quantitative intelligence – hopefully you have done a rough mental tally of that hoard of yours in the shopping cart. When you throw in personality, it really gets interesting. Because a conscientious person would follow a shopping list, wouldn’t they? So, no need for their working memory to be taxed – just scratch the items off the list. But then their perceptual reasoning comes into play – how to get to navigate to the desired items in the fastest possible time in this giant store and get out. Experiments with college students taking personality and intelligence tests show results which make personality and intelligence look like oil and vinegar dressing in your salad. You mix them in, they stick and then quickly separate. However, in everyday life, personality and intelligence do work in synchrony - for your success.

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