Personality Characteristics of Volunteers for Psychological Studies

The problem of volunteer bias is seen in terms of the unrepresentativeness or atypicality of the subjects who participate in psychological studies. Findings from investigations of the personality characteristics of volunteers are examined under the headings of: (i) unconventionality, (ii) adjustment, (iii) anxiety, (iv) social extraversion, and (v) need achievement. The percentage volunteering response in the invitation situation may be raised or lowered by incentive or restraint factors. The mean percentage volunteering response in the studies reviewed was 37 per cent. Though studies relating volunteer characteristics specifically to particular distortions in experimental data are few, emphasis has frequently been placed on the potential danger of bias from volunteer subjects. A distinction may possibly be made between volunteering as an expressed willingness to participate, and volunteering as actual participation in the experimental situation. Most volunteer bias studies have, in fact, centred on expressed-willingness volunteering. It is not yet possible to provide adequate experimental controls based on the prediction of direction and magnitude of sources of volunteer bias in specific laboratory studies.