Intelligence and personality
Intelligence and personality have some common features; for example, they both follow a relatively stable pattern throughout the whole of an individual’s life, which is genetically determined in different degrees. In addition, they are both significant predictors of various outcomes, such as educational achievement, occupational performance, and health. However, the traditional view in psychology is that there is no meaningful relationship between personality and intelligence and they should be studied as separate entities.
Firstly, intelligence is considered to be a cognitive process, while personality is recognised as being non-cognitive, and this implies that there is a great distinction between personality and intelligence. However, other psychologists argue that the distinction between cognitive and non-cognitive is vague because almost all personality traits have cognitive attributes, although they are more obvious in some traits than in others. For example, neuroticism is a personality trait, but is also related to rumination and compulsive thinking about possible threats, while agreeableness is associated with understanding and considering the mental state of others.
In addition, different methods are generally used to assess intelligence and personality. Intelligence is normally measured by means of ability tests, whereas personality is usually assessed by means of questionnaires. Furthermore, different typical measurements lead to another conceptual distinction, which is that intelligence is considered to indicate individuals’ maximal performance, while personality is believed to reflect their typical behaviour. However, others argue that multiple methods can be used to assess intelligence and personality; for example, questionnaires that require to be rated by self, peers or observers can also be used to measure individuals’ mental ability, although these kinds of measurement may lack accuracy. Therefore, different typical methods cannot prove that the relationship between intelligence and personality is a meaningless one. In addition, since individuals’ ability can also affect their typical behaviour, IQ can predict outcomes related to aspects such as performance at work, academic achievement, and health. Therefore, ability tests can provide indices of both maximal performance and typical behaviour.
An increasing number of studies have recently explored the relationship between intelligence and the Big Five personality traits.
Openness shows the strongest positive relationship with g among the Big Five personality traits, ranging from r=.06 to r=.42. Individuals with a high level of openness enjoy the experience of learning and prefer an intellectually stimulating environment. Therefore, openness shows a significant moderate association with crystallized intelligence (r=.30), but a non-significant low association with fluid intelligence (r=.08), and these results are consistent with those of other studies.
Some psychologists have recently pointed out that previous instruments used to measure openness actually assessed two distinctive aspects. The first is intellect, which reflects intellectual engagement and perceived intelligence and is marked by ideas, while the second is emotion, which reflects the artistic and contemplative qualities related to being engaged in sensation and perception and is marked by fantasy, aesthetics, feelings and actions. On this basis, intellect was found to be associated with the neural system of the working memory, which is related to g, whereas openness was not. In addition, according to a study of genetic behaviour, intellect is genetically closer to intelligence than openness.
The association between conscientiousness and intelligence is complex and uncertain. Individuals with a lower level of intelligence are always assumed to tend to behave in an orderly fashion and do extra work, which is related to being conscientious, in order to compensate for their lower level of cognitive ability. However, although intelligence has been observed to be negatively correlated with conscientiousness in some studies, others have not found this correlation to be significant and have even found a positive relationship.
Furthermore, some interaction has been found between conscientiousness and intelligence. Conscientiousness has been found to be a stronger predictor of safety behaviour in individuals with a low level of intelligence than in those with a high level. This interaction may also be found in educational and occupational settings in future studies. Therefore, relatively speaking, an increase in either conscientiousness or intelligence may compensate for a deficiency in the other.
The results of a meta-analysis research conducted in 1997, which consisted of 35 studies, indicated that there is a very small, but statistically significant positive correlation between Extraversion and g (r=.08). Another recent meta-analysis of extraversion, which comprised 50 new studies, reported a similar correlation (r=.05).
There are some moderating variables in the relationship between extraversion and g including differences in the assessment instruments and samples’ age and sensory stimulation; for example, no meaningful correlation was found between extraversion and intelligence in the samples of children. Furthermore, Bates and Rock (2004) used Raven’s matrices and found that extraverts performed better than introverts with increasing auditory stimulation, whereas introverts performed best in silence. This result is consistent with that of Revelle et al. (1976). In addition, different measures and different sub-traits of extraversion have been found to cause significantly different correlations.
Neuroticism has been found to have a reliable negative association with g(r=-.33). However, other researchers have recently reported a lower coefficient of .09 for general mental ability and emotional stability. Although these studies have some differences, they all indicate that intelligence increases with a decrease in negative emotion.
One of the reasons for this negative correlation is Test anxiety, which refers to the psychological distress experienced by individuals prior to, or during, an evaluative situation. This is closely associated with neuroticism  and has a negative influence on individuals’performance in an intelligence test (r=-.23).
Some argue that all the aforementioned evidence indicates that neuroticism is related to test performance rather than true intelligence. However, according to the results of a longitudinal study recently conducted by Gow et al., (2005), neuroticism influences an age-related decline in intelligence and there is a small negative correlation between neuroticism and a change in the level of IQ (r=-.18). Although it is still debatable if neuroticism reduces general intelligence, this study provided some valuable evidence and a direction for research. In addition, some interaction between intelligence and neuroticism has been found. Individuals with a high level of neuroticism demonstrated a poor performance, health, and adjustment only if they had a low level of intelligence. Therefore, intelligence may act as a buffer and compensate neuroticism in individuals.
No significant association between agreeableness and g has been found in previous research. However, some components of agreeableness have been found to be related to intelligence. For example, aggression is negatively associated with intelligence (r is around -.20)  because unintelligent people may experience more frustration, which may lead to aggression  and aggression and intelligence may share some biological factors. In addition, emotional perception and emotional facilitation, which are also components of agreeableness, have been found to be significantly correlated with intelligence. This may be because emotional perception and emotional facilitation are components of emotional intelligence and some researchers have found that emotional intelligence is a Second-Stratum Factor of g.
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