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).
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.
Comments, criticism, suggestions for additions or deletions, etc. should be sent to
William Revelle, Director
Graduate Program in Personality
Department of Psychology