Effect of a stimulus control intervention on attendance at a university fitness center.

The purpose of the present study was to determine the isolated effects of stimulus control on attendance at a fitness facility. Participants were members of a university fitness club randomly assigned to control (n = 50), placebo (n = 50), and stimulus control (n = 100) conditions. The control condition received no intervention, the placebo condition received a letter by mail, and the stimulus control condition received the same letter by mail plus a complimentary "EXERCISE" key chain, which was to act as the stimulus control. Attendance was monitored surreptitiously for 5 weeks baseline and 8 weeks postintervention by using the facility's computer system. A manipulation check found that 48 of the 100 participants used the key chain. Therefore, analyses were conducted separately for "intention to treat" and "actual treatment" conditions. Repeated measures multivariate analyses of variance revealed no main or interaction effects involving experimental condition in either the "intention to treat" or "actual treatment" analyses. Discussion focused on explanations for why the stimulus control intervention was not successful, and directions for future research were provided.