Monetary incentive, age, and cognition.

Results from studies of cohort differences suggest that older and younger volunteers may differ in aspects other than age. In this study subjects, who had or had not been promised $10.00 payment for their participation, were compared on certain personality and intelligence factors. No differences between incentive conditions were observed for 2466 potential subjects on willingness to participate, nor for 591 subjects eventually tested on their scores on the Primary Mental Abilities Test, the Test of Behavioral Rigidity and Cattell's 16 PF. However, differences by incentive condition were observed on the intercorrelation matrices for women on Form B of the 16 PF. Results of these analyses suggest that, with few exceptions, supplying a monetary incentive to induce subjects to participate in a study does not significantly alter the characteristics of a volunteer sample with regard to age or sex.