The double-edged sword of rewards for participation in psychology experiments
This quasi-experimental study examined participation rates and sample characteristics of participants recruited with and without the offer of course credit. In Sample 1, where course credit is not usually offered, credit was added in one condition (N =195) and not in the other (N = 175). In Sample 2, where credit is usually offered, it was maintained in one condition (N = 92) and removed in the other (N = 178). Results in both samples revealed that participation rates were higher in the credit conditions; they plunged when customary rewards were taken away. Results also revealed evidence of sample bias. More specifically, the motivational characteristics of participants and nonparticipants differed in all conditions except the new credit condition.
Sharp, Elizabeth C., Luc G. Pelletier, and Chantal Lévesque. "The double-edged sword of rewards for participation in psychology experiments." Canadian Journal of Behavioural Science/Revue canadienne des sciences du comportement 38, no. 3 (2006): 269.
Canadian Journal of Behavioural Science