249 British Journal of Psychology (2004), 95, 249–264 q 2004 The British Psychological Society www.bps.org.uk A possible model for understanding the personality– intelligence interface Tomas Chamorro-Premuzic1 and Adrian Furnham2 * 1 Department of Psychology, University of Bath, UK Department of Psychology, University College London, UK 2 Despite the recent increase in the number of studies examining empirical links between personality and intelligence (see Hofstee, 2001; Zeidner & Matthews, 2000), a theoretical integration of ability and nonability traits remains largely unaddressed. This paper presents a possible conceptual framework for understanding the personality– intelligence interface. In doing so, it conceptualizes three different levels of intelligence, namely, intellectual ability (which comprises both Gf and Gc), IQ test performance and subjectively assessed intelligence (a mediator between personality, intellectual ability and IQ test performance). Although the model draws heavily upon correlation evidence, each of its paths may be tested independently. The presented model may, therefore, be used to explore causation and further develop theoretical approaches to understanding the relation between ability and nonability traits underlying human performance. There has been a renewed interest in the last 10 years in the relationship between personality and intelligence. This interest is re¯ected in several books and reviews (Barratt, 1995; Collis & Messick, 2001; Saklofske & Zeidner, 1995; Sternberg & Ruzgis, 1994; Zeidner & Matthews, 2000), as well as empirical studies examining ability and nonability individual differences in human performance, especially in academic settings (Busato, Prins, Elshout, & Hamaker, 2000; Chamorro-Premuzic & Furnham, 2002, 2003a, 2003b; De Fruyt & Mervielde, 1996; Goff & Ackerman, 1992; Rindermann & Neubauer, 2001; Siepp, 1991). In addition, researchers have also looked at subjectively assessed intelligence (SAI ) and its relationship to personality traits and psychometric or measured intelligence (see Furnham, 2000; Furnham & Chamorro-Premuzic, in press; Furnham, Kidwai, & Thomas, 2001; Furnham & Rawles, 1995; Rammstedt & Rammsayer, 2000, 2001). Although the interest in the relationship between personality, SAI and psychometric intelligence may re¯ect an attempt to provide sound empirical evidence for the integration of fundamental ability and nonability traits, only a few researchers (e.g. Ackerman, 1996a, 1996b, 1997; Cattell, 1971, 1987; Eysenck & Eysenck, 1985; Matthews, 1974, 1999) have attempted to provide a theoretical framework for * Correspondence should be addressed to Professor Adrian Furnham, Department of Psychology, University College London, 26 Bedford Way, London WC1E OAP, UK (e-mail: a.furnham@ucl.ac.uk). 250 Tomas Chamorro-Premuzic and Adrian Furnham integrating and explaining the results of either experimental or psychometric investigations. Furthermore, there are few models or theories that attempt to describe the processes or mechanisms by which personality traits may affect intelligence test performance/outcome (Zeidner, 1995, 1998). The present paper presents a possible conceptual model for the integration of intellectual ability, personality traits, SAI and cognitive performance, after examining the salient literature in the ®eld and/or describing the processes by which these variables may interact. Personality In the area of personality structure, most researchers have agreed on the psychometrical advantages of the Big Five model proposed by Costa and McCrae (1992), often concluding that the Five Factor model is ubiquitous (Costa, 1997; Costa & McCrae, 1992; Deary & Matthews, 1993; McCrae & Costa, 1997b). According to this model, there are ®ve higher order personality traits (or factors), namely Neuroticism, Extraversion, Openness to Experience, Agreeableness and Conscientiousness, on which people differ. These individual differences refer to stable patterns of behaviour or tendencies, which are independent of each other. Neuroticism can be described as the tendency to experience negative emotions, such as anxiety, depression and anger. Extraversion refers to high activity, assertiveness and a tendency toward social behaviour. Openness to Experience represents the tendency to get involved in intellectual activities, and a preference for novel ideas and experiences. Agreeableness (also known as Sociability) refers to friendly, considerate and modest behaviour. Conscientiousness is associated with ef®ciency, determination, responsibility and persistence (see Busato et al., 2000; Costa & McCrae, 1992; Matthews & Deary, 1998 for a fuller description). Intelligence Most theories of intelligence are based on hierarchical models. These were originated by Spearman (1904, 1927), who proposed that intelligence consisted of a general ( g) factor as well as a set of speci®c (s) factors. In¯uenced by the work of Spearman (1904, 1927), R. B. Cattell (1971) elaborated one of the most prominent theories of intelligence, distinguishing between ¯uid (Gf ) and crystallized (Gc) intelligence. Broadly speaking, Gf represents information-processing and reasoning ability, that is, inductive, conjunctive, disjunctive reasoning capability used to understand relations and abstract prepositions (Stankov, 2000). By contrast, Gc is used to acquire, retain, organize and conceptualize information rather than information-processing. Whereas Gf is dependent on the ef®cient functioning of the central nervous system, Gc is dependent on experience and education within a culture. Accordingly, tests of Gf require little previous knowledge or learning on part of the examinee, whereas measures of Gc emphasize previous knowledge and education. A useful metaphor to understand the relationship between Gf and Gc, as well as their meaning, is that of a computer. Gf would represent the processor, memory and other characteristics of the individual. Gc would be equivalent to the data and information contained in the ®les and other software. Hence Gf, like the processor of a computer, refers to processes rather than content. Conversely, Gc, like the data ®les and software that are stored and loaded onto a computer, would refer to content (or information) rather than processes. Measuring both Gf and Gc is bene®cial in the sense of indicating both a Personality and intelligence 251 person’s learning potential and also his/her accumulated learning (Stankov, Boyle, & Cattell, 1995). Top-down approaches R. B. Cattell (1971, 1987) conceived personality and intelligence as separate individual difference factors and predictors of human behaviour. Thus, both variables could have a joint in¯uence on academic, work-related or social behaviour. Indeed, Cattell’s personality inventory, the 16PF (which is related to the Big Five; H. E. Cattell, 1995) included a measure of intelligence. Although this conceptualization posits that personality and intelligence should be kept separate (as they are clustered and unrelated), it also implies that certain types of behaviour (notably performance) may not be classi®ed under the domain of personality or intelligence, but of necessity as a mix of both. Accordingly, IQ test results, which are obtained through performance, cannot be considered a `pure’ measure of intelligence (for performance may also be in¯uenced by personality traits; see Strelau, Zawadzki, & Piotrowske, 2001). This approach, which posits that nonability factors may affect the results of IQ tests, is often referred to as topdown (Rindermann & Neubauer, 2001). A typical example is anxiety, which is likely to impair test performance, particularly under arousing situations (Zeidner, 1995). However, because a diversity of variables, from test conditions and distractibility to physical illness, may have a signi®cant in¯uence on the test results, problems arise when it comes to interpreting the results of IQ tests (as we cannot assume that the score is a true re¯ection of the tested person’s ability). As a consequence, top-down approaches deny the essence of the measurement of intelligence. This problem was already considered by Wechsler (1950), who proposed that IQ tests should be designed to include (rather than exclude) nonability factors; in doing so, they would not only facilitate interpretation, but also increase validity with regard to other types of performance. Nevertheless, Wechler’s advice appears to have had little or no effect on most test constructors, administrators and testers. Investment theories Another main aspect of R. B. Cattell’s (1971, 1987) theory, namely investment, deals with the in¯uence of personality on `actual’ ability, rather than IQ test results. In this respect, it is important to understand Cattell’s own distinction between ¯uid (Gf ) and crystallized (Gc) intelligence. A common de®nition is that of Gf as `the neurological structures and processes underlying mental activity’, and Gc as `the sum of acquired knowledge and experience’ (Rolfhus & Ackerman, 1996, p. 175) (other de®nitions are given above). Furthermore, Cattell also believed Gc to be the result of applying Gf over time. Accordingly, individual differences in Gc could be determined by the amount and quality of investment of Gf. This theory was further developed by Ackerman (1996a, 1996b, 1999), who distinguished between intelligence as processes (Gf ) and intelligence as content/knowledge (which is similar, but not equivalent, to Gc). Like Cattell, Ackerman views intelligence as partly the result of engaging (investing) in intellectual activities. However, more emphasis is placed on the role of personality, interests and motivation in determining the acquisition of knowledge (see Ackerman’s theory of PPIK, i.e. Intelligence as Process, Personality, Interests and Knowledge). Thus theories of investment are concerned with the cognitive processes and nonability traits that underlie the development of human intellect in a broad sense. 252 Tomas Chamorro-Premuzic and Adrian Furnham Intellectual ability and IQ test performance It should be noted that the top-down and investment approaches to the personality ± intelligence interface seem to refer to different conceptualizations of intelligence. Whereas the top-down approach is concerned with intelligence as measured by IQ test performance ( here personality traits can modify the results of IQ tests rather than `actual’ intelligence), investment theories are concerned with `actual’ ability (here personality traits can partly determine the development of intellectual ability rather than merely in¯uence IQ test performance). Hence, there are at least two connotations for intelligence, one refers to ability as a trait (`actual’ intelligence), the other to ability as output (cognitive or IQ test performance). Whereas investment theories deal with how the intelligence trait or `actual’ intelligence develops, top-down approaches are merely concerned with performance on IQ tests. Thus theoretical approaches to the personality± intelligence interface will differ according to their representation of ability as a trait or ability as output or performance (though the two are related). Subjectively assessed intelligence (SAI)1 Although researchers have generally opted for ability tests, intelligence can also be assessed in different ways. A typical example is that of lay people, who assess their own and others’ intelligence on the basis of several nonpsychometric criteria (income, academic performance, life and job success, social skills, etc). Whereas standardized tests are regarded as an objective method (they represent a well-established approach not only in academic psychology but also in applied areas such as occupational and educational settings), self and others’ estimations represent a subjective form of assessment. Thus SAI may be considered a different type of intelligence than psychometric. Eysenck and Eysenck (1985) argued that SAI should be considered part of personality rather than intelligence. This idea is consistent with Cronbach’s (1949) conceptualization of maximal and typical performance measures, as well as the tradition in individual differences to assess personality through self-reports and intelligence through objective performance tests. Although researchers have preferred to assess ability through psychometric tests rather than SAI, several studies have indicated that SAI (and related constructs) are signi®cant predictors of IQ test performance (e.g. Furnham & Chamorro-Premuzic, in press; Furnham & Rawles, 1995, 1999). Furthermore, there is evidence for a signi®cant relationship between SAI and established personality traits (®ndings presented below). Accordingly, SAI represents another approach to the relationship between personality and intellectual ability. Integrating theories and Žndings We thus have three distinct concepts (or aspects) of intelligence: intellectual ability, which comprises both Gc and Gf, IQ test performance or intelligence as output, and SAI (self/other estimates). Figure 1 presents a possible model for the integration of these three levels with the Big Five personality traits. The rest of the paper discusses each path 1 Although the terms SAI and self-estimates of intelligence may be treated as interchangeable,SAI may also be used to refer to estimations of others’ (as opposed to one’s own) intellectual abilities. Personality and intelligence 253 Figure 1. A model for understanding the personality–intelligence interface. of the model. It is noteworthy that the focus of this paper is the relationship between personality and intelligence. At this stage, the proposed model will not attempt to integrate numerous other variables such as gender, age, motivation, time of the day, menstrual cycle, task demands, attitudes and conceptions of intelligence, which, albeit important, are not regarded as essential to explain interactions between personality and intelligence. Intellectual ability and IQ test performance Paths 1a and 1b of Fig. 1 are primarily concerned with the relationship between intelligence and cognitive performance. To this end, it is necessary to emphasize the theoretical distinction we made between `actual’ intellectual ability, i.e. Gf and Gc (in broad terms, the ability to reason about novel problems and apply previously acquired knowledge), and IQ test performance. Although this distinction may be operationally inconvenient (because it implies that intelligence cannot be measured directly), it is crucial in order to understand how the above variables relate in our model. Furthermore, it should be noted that, although we propose a conceptual differentiation between `actual’ intelligence and IQ test performance, we believe that established IQ tests/ability measures, are reasonably good indicators of a person’s intellectual ability (capacity): that is, they show construct and predictive validity (Deary, 2001). In fact, correlational evidence for the predictive validity of ability tests with regard to real-world performance is usually regarded as evidence that ability/IQ tests are sound indicators of intelligence (see Barrick & Mount, 1991; Gottfredson, 1997; Hunt, 1999; Hunter & Hunter, 1984; Schmidt, Ones, & Hunter, 1992). Hence, it is also implied that most of the variance in IQ/ability measures is accounted for by intelligence. Most, but not all. As Goff and Ackerman (1992) noted (see also Ackerman & Heggestad, 1997; Matthews, Davies, Westerman, & Stammers, 2000; Sarason, Sarason, & Pierce, 1995), temperamental factors make `actual’ ability different from `maximal’ ability ( IQ test performance). This distinction is not due to any disagreement on how intelligence is measured, but merely to emphasize the performance aspects that are inherent of any IQ test completion. Accordingly, paths 1a and 1b illustrate the in¯uence of intellectual 254 Tomas Chamorro-Premuzic and Adrian Furnham ability that is, Gf and Gc, on cognitive performance, speci®cally IQ tests (although any indicator of variability in occupational, academic and task-speci®c measure could be inserted in this section). As stated above, we believe that IQ tests, as much as they represent reliable and valid measures of intelligence, should be considered part of performance, and that, like other types of performance (and even more so), performance on these tests is primarily affected by a person’s intellectual ability. Thus, if we asked why some people score higher on mental tests than others, we could answer `because they are more intelligent’ (although, as we discuss below, IQ tests performance may also be in¯uenced by personality traits). SAI and performance Path 2 of Fig. 1 is concerned with the relationship between SAI and IQ test performance. As can be observed, SAI (self/other assessed in the Eysenckian system; Eysenck & Eysenck, 1985), like Gf and Gc, is placed as a predictor of performance. Although the predictive power of SAI may be considerably lower than that of IQ tests, it has been shown that SAI predicts exam performance. Thus, believing one is intelligent when in fact one is not will not in¯uence test scores much, whereas the opposite pattern (low SAI and high IQ) might. This phenomenon is usually referred to as `expectancy effect’, and has been found in a number of related constructs, e.g. self-monitoring (Stankov, 1999), selfhandicap (Rhodewalt, 1990), self-evaluation (Flett, Hewitt, Blanckstein, & Gray, 1998; Morris & Liebert, 1969), self-motivation (Zeidner, 1995), self-ef®cacy (Bandura, 1986; see also Ackerman, 1997; Matthews, 1999), locus of control (Braden, 1995), self-concept (Rindermann & Neubauer, 2001), self-esteem and self-con®dence (Koivula, Hassmen, & Fallby, 2002). The advantageof assessing SAI rather than the above-listed constructs is that SAI refers speci®cally to a person’s intellectual ability, whereas the other constructs may be indicative of the person’s subjective appraisal on other, often more general, domains. Accordingly, SAI may be used as both a predictor of IQ test scores and an indicator of feedback or the accuracy of a person’s insight into his/her intellectual ability. In the last decade research has consistently provided correlational evidence for the relationship between SAI and IQ test performance (see Furnham, 2001 for a review on the topic). Because ability tests are fairly good indicators of people’s intelligence (see paths 1a and 1b), it can be concluded that people have some insight into their intellectual ability (see also Borkenau & Liebler, 1993; Paulhus, Lysy, & Yik, 1998). Hence we would expect SAI to be a signi®cant predictor of human performance, particularly on IQ tests. However, path 2 also represents the hypothesis that people’s SAI may be in¯uenced by their actual performance. In other words, when people estimate their intellectual ability they also take into account their previous performances (not just on IQ tests, but also on occupational and academic assignments). Thus SAI is partly dependent on the frequency and veridicality of feedback, which may explain why studies have found that SAI could be signi®cantly predicted by previous IQ test-experience (see Furnham, Chamorro-Premuzic, & Mouta®, 2003). Further evidence for this hypothesis would be provided by research looking at how evaluation of different performance indicators is related to the lay theories of intelligence underlying people’s SAI. In this respect, it is important to examine speci®c aspects of people’s conceptions of intelligence, such as genderÐas males tend to give/receive higher SAI than females (see Furnham, Clark, & Bailey, 1999; Furnham & Gasson, 1998; Reilly & Mulhern, 1995). To the extent that Personality and intelligence 255 people’s conceptions of intelligence may in¯uence their SAI, they may also have a signi®cant effect on performance, particularly on IQ tests. This effect may be particularly evident in situations in which the results of the tests have little or no consequences for the participant (for instance, when participants are college students). We could expect that in these situations people who have negative attitudes towards IQ tests (e.g. believe that intelligence cannot be assessed by those tests) may reduce their effort and deliberately under-perform. Personality traits and IQ test performance Paths 3a and 3b refer to the in¯uence of personality traits on cognitive performance. Although the association between personality and performance is not novel, most of the literature has been concerned with the relationship between personality traits and academic or occupational, rather than IQ test, performance. Moreover, performance has been traditionally related to ability rather than personality (Harris, 1940; Hunter & Hunter, 1984; Matthews et al., 2000; Zeidner & Matthews, 2000). Despite this, personality inventories are widely used in selection and recruitment. For instance Blinkhorn and Johnson (1990) reported that around 50% of companies in the UK were using them in the late 1980s, in addition to their use in vocational guidance, counselling, school and college placement (Zeidner & Matthews, 2000). Without undermining the importance of intellectual ability in human performance, research in the last 10 years has yielded important evidence for the signi®cant predictability of academic performance by personality traits (Barrick & Mount, 1991; Busato et al., 2000; De Fruyt & Mervielde, 1996; Goff & Ackerman, 1992; Rinderman & Neubauer, 2001; Salgado, 1997; Siepp, 1991). With regard to academic performance, we found that personality traits were signi®cant predictors of academic achievement in university, in some cases accounting for almost 30% of the variance in ®nal examination grades (Chamorro-Premuzic & Furnham, 2003a, 2003b). More speci®cally, we found that Neuroticism and Extraversion are both negative predictors of success, whereas Conscientiousness is a positive (and probably the most important) predictor of academic achievement (Chamorro-Premuzic & Furnham, 2003a, 2003b; see also De Fruyt & Mervielde, 1996). With regard to the relationship between personality traits and IQ test performance, results have suggested that there are signi®cant but modest links between IQ scores and some of the Big Five traits. In a meta-analysis of more than 130 studies, Ackerman and Heggestad (1997) reported that intelligence was signi®cantly correlated with Neuroticism …r ˆ 2:15†; Extraversion …r ˆ :08† and Openness to Experience …r ˆ :33†: The results of two other large studies (Mouta®, Furnham, & Crump, 2002; Mouta®, Furnham, & Patiel, 2003) indicated that intelligence is also negatively and signi®cantly correlated with Conscientiousness. It has been argued that Neuroticism and Extraversion affect test performance rather than `actual’ intelligence (Zeidner & Matthews, 2000). The negative association between Neuroticism and IQ scores would be explained primarily in terms of the likelihood of neurotic individuals experiencing anxiety and stress during arousing conditions such as an IQ test or academic examinations. The positive relationship between Extraversion and IQ test results would be a re¯ection of extraverts’ higher speed of response and assertiveness, which may be considered an advantage in most types of psychometric tests. In addition, extraverts’ 256 Tomas Chamorro-Premuzic and Adrian Furnham lower level of arousal would mean they are less likely to be distracted by background noise or speech (which could be advantageous under certain testing conditions). Personality traits and SAI Paths 4a, 4b, 4c and 4d depict the relationship between personality and SAI. Eysenck and Eysenck (1985) argued that SAI should be conceptualized as part of personality rather than intelligence. There is evidence for the signi®cant relationship between SAI and Neuroticism (negative), Extraversion (positive) and Openness (positive) (see Furnham & Chamorro-Premuzic, in press; Furnham et al., 2001). These results indicate that personality traits are more related to SAI than to IQ test performance. It may thus be suggested that personality traits in¯uence people’s insight into their intellectual abilities, for their estimations are likely to be affected by nonability factors (that are only modestly and often not signi®cantly related to IQ test performance). Accordingly, it is likely that SAI may act as a mediator variable between personality and IQ test performance. Individuals high on Neuroticism are likely to underestimate their intelligence (see 4a) as they have a general tendency to make negative self-related judgments (see Matthews et al., 2000; Wells & Matthews, 1994). As noted (3a), this is likely to impair actual performance. The opposite can be said for Extraversion, as extroverted (like stable) individuals are assertive and thus likely to report higher SAI (Furnham et al., 2001). If extraverts are more con®dent and optimistic approaching a task or problem, their positive outlook may be likely to feed into higher performance (Zeidner & Matthews, 2000). With regard to Openness (see 4c), the relationship to SAI is likely to be more complex (see Brand, 1994; Goldberg, 1994; Hofstee, 2001; Johnson, 1994; Saucier, 1994) we have proposed (in agreement with Hofstee, 2001; see also Goff & Ackerman 1992) that there is a considerable conceptual overlap between the concept of SAI and Openness (Chamorro-Premuzic, Mouta®, & Furnham, 2003). This overlap can be explained by interpreting Openness as a self-report measure of typical, as opposed to maximal (see Cronbach, 1949; Hofstee, 2001), intelligence, particularly of Gc. Hence Openness, like SAI, is self-assessed and refers to people’s reported (rather than objectively measured) intelligence. It should be noted that IQ test results are usually correlated at r ˆ :30 with both Openness (Ashton, Lee, Vernon, & Jang, 2000; McCrae & Costa, 1985) and SAI (Furnham & Chamorro-Premuzic, in press; Furnham & Rawles, 1995, 1999). Nevertheless there are a number of conceptual differences between Openness and SAI (McCrae & Costa, 1997a, 1997b). Primarily these would refer to aspects of Openness, such as artistic orientation and aesthetic sensitivity, which are not tapped by SAI. Further, whereas SAI items assess estimations of a score, Openness items assess preference for activities or behavioural tendencies. It is therefore argued that personality traits are important in shaping people’s estimations of their intellectual ability. To the extent that people’s personality affects their estimations of their intellectual ability, and considering that these estimations affect actual performance, we propose that SAI is a mediator variable between personality and performance (including performance on IQ test). Although many personality theorists argue that traits are biologically based and stable over time, the aetiology and stability of SAI are not clear. Dweck’s (1999) work on `self-theories’ (speci®cally beliefs about the stability of intelligence) suggests that even primary school children have clear beliefs about their own personal abilities. Children who are entity Personality and intelligence 257 theorists believe intelligence is ®xed, whereas those who are incremental theorists, believe it is malleable. The former believe performance re¯ects effort irrespective of task dif®culty and effort, the latter that it primarily re¯ects efforts and strategies to complete the task. These beliefs are self-ful®lling and stable over time. One factor that may effect SAI is actual IQ test taking experience and feedback. Thus Furnham and Ward (2001) found people who had taken IQ tests consistently gave higher self-estimates. Self-rated intellectual abilities are no doubt a function of primary and secondary socialization, and may only become fairly stable in middle to late adolescence. However, it seems quite possible that beliefs would change as a function of getting evidence, for instance, in the form of exam performance that contradicts self-estimates. It maybe easier to persuade people with low self-estimates that they should be higher than the other way around, because of the possible protective nature of these beliefs (Dweck, 1999). Intellectual ability and personality traits Finally, paths 5a and 5b refer to the relationship between personality and intellectual ability (Gf and Gc). As noted, indirect evidence for this relationship has been derived from correlational studies looking at the relationship between personality traits and IQ test results (top-down approaches). Paths 3a and 3b were referred to the effects of personality traits (Neuroticism and Extraversion) on IQ test performance, whereas paths 5a and 5b are concerned with investment or developmental links among Conscientiousness, Openness, Gf and Gc. It is now time to ask whether personality traits have any effect on the development of intellectual skills (and vice versa). This refers to the question of why some people are more able than others (rather than why some people score higher on IQ tests than others). In their recent review, Zeidner and Matthews (2000) concluded that although IQ test performance `may be in¯uenced by an array of non-cognitive states (fatigue, anxiety, arousal) ( : : : ), at the level of latent constructs, IQ and personality are orthogonal constructs’ (p. 585) (see also Eysenck, 1994). However, R. B. Cattell (1971, 1987) and Ackerman (1996a, 1996b, 1999) proposed that some personality traits may play a signi®cant role in the processes of intellectual skill acquisition, in the sense that they may in¯uence choices to engage (invest) in particular domains. In particular, the trait Typical Intellectual Engagement (TIE), which includes aspects of Openness and Conscientiousness, is a clear example of how individual differences in nonability traits (curiosity, interests, perspective) can in¯uence ability traits (Gc, knowledge) to result in a trait complex (intellectual/cultural). In Ackerman’s view, personality traits are important components of the equation which determines whether an individual acquires knowledge and skills within a speci®c domain (Rolfhus & Ackerman, 1996). Evidence for Ackerman’s theory can be found, indirectly, in the signi®cant correlations between TIE and performance on Gc tests (Ackerman & Goff, 1994; Goff & Ackerman, 1992), but also, directly, in experimental studies suggesting that training may improve abilities (Ackerman & Humphreys, 1990). Hence the decision to engage in intellectually bene®cial activities may mediate the relationship between personality traits and the development of adult intellectual ability, particularly Gc. In this way, personality traits (notably TIE and Openness) may in¯uence actual intelligence (5a). By contrast, the model also includes a path (5b) that conceptualizes the in¯uence of actual intelligence (Gf ) on personality traits, notably Conscientiousness. Speci®cally, it is 258 Tomas Chamorro-Premuzic and Adrian Furnham argued that low intellectual capacity would tend to lead to high Conscientiousness, and vice versa. The rationale underlying the negative relationship between Conscientiousness and measures of Gf is that less able individuals in a competitive educational or work environment may become more conscientious over time as a way of compensating for their relatively low intellectual ability (Mouta® et al., 2002, 2003). Conversely, one may expect highly able (high Gf ) people to have a lower tendency to develop a conscientious (e.g. dutiful, organized, responsible) personality, and rely on their native ability, as their high intellectual competence would be suf®cient to achieve their goal. However, experimental problems may arise when participants are given a measure of Gf (or intelligence in general) in situations in which the results have no signi®cant consequences for them. A typical example would be that of opportunity samples (such as university students run in tutorials or compulsory testing hours). In those situations, one may expect conscientious participants to take the task more seriously than low conscientious participants, levelling with their efforts their lack of intellectual competence. Furthermore, one may assume that in samples composed of selected university students there is a considerable restriction of range in intellectual ability (as students have been admitted on the basis of their previous academic attainment). Although this hypothesis may be regarded as a mere assumption, it may explain the fact that no published papers have reported negative and signi®cant correlations between Gf and Conscientiousness on opportunity samples (or in situations in which participation had no relevant consequences for the subjects). However, there are few (but robust) studies reporting this effect in participants (e.g. job applicants) who may be assumed to have been highly motivated to obtain high scores on ability tests (see Mouta® et al., 2002, 2003). It is noteworthy that other personality traits may be affected by intelligence as capacity. Such is the case of Openness to Experience and Extraversion (although more modestly). Actual intellectual capacity (specially Gf ) may in¯uence both Openness (positively) and Extraversion (negatively). In the case of Openness, one may wonder to what extent high Gf may be a precondition of high Openness (in that it may predispose the development of intellectual interests, intellectual curiosity, and intellectual personality in general). This hypothesis may be better understood in terms of adaptive models such as that proposed by Matthews (1999). In this model, the development of ability and nonability traits are explained in terms of interactions underlying equally speci®c adaptations. The bottom line to this theory is that there are different cognitive patterns for different personality traits. Traits may thus be identi®ed with adaptive and maladaptive behaviours. Accordingly, Openness may be interpreted in terms of adaptation to academic, artistic or intellectual environments. Thus both Openness and Gf may interact to support the development of skills that are bene®cial with regard to performance on tests of Gc (Ackerman & Heggestad, 1997). Individuals high on Gf would therefore be more likely to develop a more Open personality. With regard to Extraversion, hypotheses are somehow more arbitrary because there is little (if no) direct empirical support for the negative relation between Extraversion and intellectual ability. However, there is some evidence in the literature for a negative relationship between Extraversion and academic achievement (Chamorro-Premuzic & Furnham, 2003a, 2003b). Interestingly, it has been noted that the sign of the correlation between Extraversion and academic achievement changes from positive (i.e. children tend to perform better in elementary school when they are extraverted) to negative (i.e. secondary school and university students tend to obtain higher grades if they are introverted) as individuals progress through the formal educational system. Although Personality and intelligence 259 this change may be the result of differences in assessment methods (from course work or amount of participation in class, to essay writing or multiple-choice exam papers), or the replacement of an easy and predominantly social atmosphere by the rather formal atmosphere of secondary school (Eysenck, 1994), it has also been suggested that this change may re¯ect the fact that the less able individuals become extraverted and vice versa (Anthony, 1973). In this sense, highly intellectually able students would be more likely to adopt more serious study habits, whereas the less able ones would have a greater tendency to socialize and relate to others. Hence there may be other ways in which Gf as capacity may affect personality traits, and not just the ones in Fig. 1. A central question must be how to test the model presented in Fig. 1 empirically. Ideally, this would involve giving a large, representative, population, valid measures of both ¯uid and crystallized intelligence, and personality. It would also involve an appraisal of various aspects of self-assessed intelligence including ideas about the stability of intelligence. Ideally, this may be done longitudinally, to check not only the stability of the relationships between the variables, but also how changes in SAI (probably the least stable factor) in¯uence other factors. Conclusions In a recent chapter on personality and intelligence, Zeidner and Matthews (2000) concluded that personality traits may relate to IQ test performance but not to IQ `at the level of latent constructs’ (p. 585) (see also Eysenck, 1994). Although this conclusion is well-founded on empirical evidence (such as the results of Ackerman & Heggestad’s meta-analysis), the distinction between IQ test performance and `actual’ intelligence is a rather implicit (perhaps latent) one. Owing to the overwhelming predictive power of psychometric intelligence (see, for instance, Gottfredson, 1997), `actual’ intelligence and the IQ test result are mostly considered synonyms. Accordingly, the assumption that personality traits may affect IQ test results but not `actual’ intelligence may appear inconsistent with regard to the overall literature on intelligence. However, we have argued that such a distinction is necessary when it comes to explaining personality ± intelligence interactions. Furthermore, we have presented a conceptual framework to understand the personality ± intelligence interface, based predominantly on the distinction between intelligence as IQ test results and `actual’ intelligence (Gf and Gc). Personality traits may in¯uence IQ test performance, to the extent that they are relevant with regard to stress coping strategies (like Neuroticism), or relate to test conditions, such as length and type of cognitive measure employed (like Extraversion) (see Matthews, 1999; Zeidner & Matthews, 2000). However, personality traits may also relate to actual intellectual ability. Examples of this relationship are Openness to Experience or Typical Intellectual Engagement (Goff & Ackerman, 1992), two personality traits that play a relevant role in the processes (i.e. investment; Ackerman, 1996a, 1996b; R. B. Cattell, 1971, 1987) underlying the development of adult intellectual competence and knowledge acquisition. Furthermore, it is also likely that intellectual ability may in¯uence personality traits; such is the case of Conscientiousness, a personality trait which may partly develop as a consequence of high or low intelligence capacity (see Mouta® et al., 2002, 2003). At the psychometric level, the signi®cant relationship between personality traits and both `actual’ intelligence and test performance has been evidenced in meta-analytic or large-scale studies such as Ackerman and Heggestad (1997) or Ashton et al. (2000). It is, however, important to 260 Tomas Chamorro-Premuzic and Adrian Furnham refer to a conceptual framework that differentiates between the two different aspects of intelligence, as certain personality variables may only relate to performance (i.e. Neuroticism), and others to `actual’ intelligence (i.e. Openness). A third level of intelligence was proposed by including the concept of SAI. Although the predictive power of SAI may be considerably lower than that of the IQ test, a number of related constructs, e.g. self-monitoring (Stankov, 1999), self-handicap (Rhodewalt, 1990), self-evaluation ( Flett et al., 1998; Morris & Liebert, 1969), self-motivation (Zeidner, 1995), self-ef®cacy (Bandura, 1986; see also Ackerman, 1997; Matthews, 1999), locus of control (Braden, 1995), self-concept (Rindermann et al., 2001), selfesteem and self-con®dence (Koivula et al., 2002) have provided evidence that not only objectively (or- psychometrically) assessed competences may affect performance. Furthermore, there is recent evidence for a signi®cant relationship between SAI and IQ test performance as well as personality traits (e.g. Furnham & Chamorro-Premuzic, in press). Thus SAI may be regarded as a relevant concept for understanding personality ± intelligence relationships; moreover, we have argued that SAI may mediate the relationship between personality traits and IQ test performance. The last decade has seen an unprecedented interest in the relation between personality and intelligence (Hofstee, 2001; Zeidner & Matthews, 2000). However integration of ability and nonability individual differences underlying human performance has remained largely unaddressed, particularly at the theoretical level. In the present paper, we have presented a conceptual framework for understanding the personality± intelligence interface. We believe that this framework may be of great help in understanding and interpreting empirical evidence linking personality variables to both psychometric and subjectively assessed intelligence. Furthermore, there are important implications derived from the presented model, particularly with regard to applied settings such as occupational and academic performance. Given that personality traits are likely to in¯uence both cognitive performance (for instance, on psychometric tests) and the development of `actual’ intellectual ability or adult knowledge/skill acquisition, it would seem important that assessment conducted towards the selection and placement of candidates (in both occupational and academic settings) is designed to include personality traits. First, because personality variables may affect the results of the cognitive tests on which admission decisions may be based, and, second, because the development of future skills (which are intrinsic to overall performance) may be enhanced or impaired by certain aspects of the individual’s personality. 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