Overjustification Effect - Experimental Evidence

Experimental Evidence

In one of the earliest demonstrations of this effect, Mark Lepper and Richard Nisbett selected a population of 3–5-year-old children who displayed intrinsic interest in the activity of drawing. In the experiment, they divided the children into three groups. The experimenters offered and would give the first group of children a "good player" ribbon for drawing. They offered nothing to the second group, but would give them the same reward. They did not offer and would not give anything to the third group. Later, when observed in a free-play setting, the first group engaged significantly less in the activity of drawing, while the other groups' behavior did not change. The researchers concluded that expected rewards undermine intrinsic motivation in previously enjoyable activities. A replication of this experiment found that rewarding children with certificates and trophies decreased intrinsic interest in playing math games.

Researchers at Southern Methodist University conducted an experiment on 188 female university students in which they measured the subjects' continued interest in a cognitive task (a word game) after their initial performance under different incentives. The subjects were divided into two groups. Members of the first group were told that they would be rewarded for competence. Above-average players would be paid more and below-average players would be paid less. Members of the second group were told that they would be rewarded only for completion. Their pay was scaled by the number of repetitions or the number of hours playing. Afterwards, half of the subjects in each group were told that they over-performed, and the other half were told that they under-performed, regardless of how well each subject actually did. Members of the first group generally showed greater interest in the game and continued playing for a longer time than the members of the second group. "Over-performers" continued playing longer than "under-performers" in the first group, but "under-performers" continued playing longer than "over-performers" in the second group. This study showed that, when rewards do not reflect competence, higher rewards lead to less intrinsic motivation. But when rewards do reflect competence, higher rewards lead to greater intrinsic motivation.

Richard Titmuss suggested that paying for blood donations might reduce the supply of blood donors. To test this, a field experiment with three treatments was conducted. In the first treatment, the donors did not receive compensation. In the second treatment, the donors received a small payment. In the third treatment, donors were given a choice between the payment and an equivalent-valued contribution to charity. None of the three treatments affected the number of male donors, but the second treatment almost halved the number of female donors. However, allowing the contribution to charity fully eliminated this effect.