Studies of human performance provide one of the prime methods for investigating associations between traits and objective indices of behaviour. In the laboratory, we can design tasks that assess basic cognitive functions such as speed of reaction, short-term and long-term memory, and focused attention. We can then test whether personality traits predict speed, accuracy or qualitative style of performance on such tasks. Studies of this kind contribute broadly to construct validation, by showing that traits relate to behavioural measures that are conceptually linked to the trait. For example, a scale for impulsivity should predict a pattern of fast, inaccurate responding on speeded tasks – although we may have to design the task carefully to show the expected result. Demonstrations of this kind make a major contribution to showing that questionnaire measures of traits are assessing some genuine ‘core’ psychological quality, and not just some superficial response bias.

Performance research is also of considerable applied relevance, in that trait measures may be used to predict a person's competence in a particular job or activity. For example, personality may predict accidents in transportation and industrial settings. Most of us would be reluctant to fly in an aeroplane piloted by an individual with abnormally high sensation-seeking or psychopathic tendencies, and, in fact, some airlines use the MMPI in pilot selection, to screen out applicants who may be vulnerable to mental illness (see Dolgin and Gibb, 1989).