Personality and Ability

Personality and Ability

Although to some the term personality refers to all aspects of a person's individuality, typical usage divides the field into studies of ability and personality. Tests of ability are viewed as maximal performance measures. Ability is construed as the best one can do on a particular measure in a limited time (speed test) or with unlimited time (power test). Personality measures are estimates of average performance and typically include reports of preferences and estimates of what one normally does and how one perceives oneself and is perceived by others.

The same procedures used to clarify the structure of cognitive abilities have been applied to the question of identifying the domains of personality. Many of the early and current personality inventories use self-descriptive questions (e.g., do you like to go to lively parties; are you sometimes nervous) that are rationally or theoretically relevant to some domain of interest for a particular investigator. Although there is substantial consistency across inventories developed this way, some of this agreement could be due to conceptually overlapping item pools. Other researchers have advocated a lexical approach to the taxonomic problem, following the basic assumption that words in the natural language describe all important individual differences. This shifts the taxonomic question from how are individuals similar and different from each other to how are the words used to describe individuals (e.g., lively, talkative, nervous, anxious) similar and different from each other.

Dimensional analyses of tests developed based on lexical, rational, or theoretical bases suggest that a limited number (between three and seven) of higher order trait domains adequately organize the thousands of words that describe individual differences and the logically infinite way that these words can be combined into self or peer report items. The broadest domains are those of introversion-extraversion and emotional stability-neuroticism, with the domains of agreeableness, conscientiousness and intellectual openness or culture close behind. These domains can be seen as asking the questions that one wants to know about a stranger or a potential mate: are they energetic and dominant (extraverted), emotionally stable (low neurotic), trustworthy (conscientious), lovable (agreeable), and interesting (intelligent and open).

Measures of ability and personality reflect observations aggregated across time and occasion and require inferences about stable latent traits thought to account for the variety of observed behaviors. However, there are other individual differences that are readily apparent to outside observers and require little or no inference about latent traits. The most obvious of such variables include sex, age, height, and weight. Differences that require some knowledge and inference are differences in ethnicity and social economic status. These obvious group differences are sometimes analyzed in terms of the more subtle measures of personality and ability or of real life outcomes (e.g, sex differences in neuroticism, mathematics ability, or income).

Predictive Validity

Individual differences are important only to the extent that they make a difference. Does knowing that people differ on a trait X help in predicting the likelihood of their doing behavior Y? For many important outcome variables the answer is a resounding yes. In their review of 85 years of selection in personnel psychology, Frank Schmidt and John Hunter (Psychological Bulletin, 1998, 124, 262-274) show how differences in cognitive ability predict differences in job performance with correlations averaging about .50 for mid complexity jobs. These correlations are moderated by job complexity and are much higher for professional-managerial positions than they are for completely unskilled jobs. In terms of applications to personnel psychology, a superior manager (one standard deviation above the mean ability for managers) produces almost 50% more than an average manager. These relationships diminish as a function of years of experience and degree of training. General mental ability (g) also has substantial predictive powers in predicting non-job related outcomes, such as likelihood of completing college, risk for divorce and even risk for criminality.

The non-cognitive measures of individual differences also predict important real life criteria. Extraversion is highly correlated with total sales in dollars among salespeople. Similarly, impulsivity can be used to predict traffic violations. Conscientiousness, when added to g substantially increases the predictability of job performance. Although the size of the correlation is much lower, conscientiousness measured in adolescence predicts premature mortality over the next fifty years.

  • For an amazing demonstration of the predictive validity of ability measures, the work of Camille Benbow, David Lubinski and their colleagues is a must read. See for instance
    • Lubinski, D., & Benbow, C. P. (2006). Study of Mathematically Precocious Youth (SMPY) after 35 years: Uncovering antecedents for the development of math-science expertise. Perspectives on Psychological Science, 1,316-343
    • Lubinski, D., Benbow, C. P., Shea, D. L., Eftekhari-Sanjani, H., & Halvorson, M. B. J. (2001). Men and women at promise for scientific excellence: Similarity not dissimilarity. Psychological Science, 12, 309-317. (pdf)
  • Linda Gottfredson has examined the effect of intelligence on real world criteria (e.g. income, mortality risk) and makes the point that life is an intelligence test.
    • Gottfredson, L. S. (in press). Innovation, fatal accidents, and the evolution of general intelligence. In M. J. Roberts (Ed.), Integrating the mind. Hove, UK: Psychology Press. (pdf)
    • Batty, G. D., Deary, I. J., & Gottfredson, L. S. (2007). Pre-morbid (early life) IQ and later mortality risk: Systematic review. Annals of Epidemiology. epub available December 15, 2006 (pdf).
    • Gottfredson, L. S. (2004). Life, death, and intelligence. Journal of Cognitive Education and Psychology [online], 4, (1), 23-46. pdf
  • A web based history of research on intelligence is a continuing project of Jonathan Plucker at the University of Indiana. Includes brief biographies of many of the major influences (from Plato to Jensen) in the study of intelligence. Well worth visiting!
  • Jensen, A.R. (1998) The g factor: The Science of Mental Ability Westport, CT, USA: Praeger Publishers/Greenwood Publishing Group, Inc. A comprehensive review of general mental ability by one of the leading researchers in individual differences and intelligence. (See also Jensen, A.R. (1993) Spearman's g: Links between Psychometrics and Biology. Ann N Y Acad Sci; 702: 103-29. Abstract)
  • Jensen, A.R. and associated responses. More than 44 comments and reviews of the online summary of Jensen's 'g factor'. PSYCOLOQUY
  • Neisser, U. (Ed.) 1998. The Rising Curve: Long-Term Gains in IQ and Related Measures (Apa Science Volumes), Washington, D.C. American Psychological Association. A symposium on the "Flynn Effect": the demonstration that standardized measures of IQ have risen significantly over the past 50 years.
  • For a theoretical explantion of the "Flynn Effect," see the article by Dickens and Flynn, 2001 Heritability Estimates Versus Large Environmental Effects: The IQ Paradox Resolved, in Psychological Review, 108, 346-369." Some argue that the high heritability of IQ renders purely environmental explanations for large IQ differences between groups implausible. Yet, large environmentally induced IQ gains between generations suggest an important role for environment in shaping IQ. The authors present a formal model of the process determining IQ in which people's IQs are affected by both environment and genes, but in which their environments are matched to their IQs. The authors show how such a model allows very large effects for environment, even incorporating the highest estimates of heritability. Besides resolving the paradox, the authors show that the model can account for a number of other phenomena, some of which are anomalous when viewed from the standard perspective. " (From the Abstract).
  • Hunt, E. (1995) The Role of Intelligence in Modern Society. American Scientist is a very thoughtful (and online) treatment of intelligence.
  • The 1997 issue of Intelligence is a special issue devoted to Intelligence and Social Policy. Vol 24, 1-320. See particularly:
    • Plomin, R. and Petrill, S.A. (1997) Genetics and Intelligence: What's New? Intelligence, 24, 53-78.
    • Gottfredson, L. S. (1997) Why g matters: The Complexity of Everyday Life. Intelligence, 24, 79-132.
  • Saklofske, D. H. & Zeidner, M. (1995). International Handbook of Personality and Intelligence. New York: Plenum.
  • Sternberg, R. J. & Ruzgis, P. (1994) Personality and Intelligence. Cambridge: Cambridge University Press.
  • Herrnstein R. J. and Murray, C. The Bell Curve: Intelligence and Class Structure in American Life, New York: Free Press, 1994. (reviewed in Contemporary Psychology, May 1995 by Bouchard and Dorfman.)
  • Information about achievement tests, including ERIC's test locator and a glossary of terms is available from ERIC.
  • The APA page on testing and assessment contains a set of links and articles on the use of tests in society.
  • Werner Wittman's challenge of "gMania" given at the ISSID meeting in 1997.
  • For an early description of an ambitious project to examine QTLs of IQ, see Plomin R, McClearn GE, Smith DL, Vignetti S, Chorney MJ, Chorney K, Venditti CP, Kasarda S, Thompson LA, Detterman DK, et al. (1994) DNA Markers associated with High versus Low IQ: the IQ Quantitative Trait Loci (QTL) Project. Behav Genet 1994 Mar; 24(2): 107-118 (Abstract)
  • The Heritability of IQ Remains High throughout the Lifespan:
  • Recent publications available online: