The overjustification effect occurs when an expected external incentive such as money or prizes decreases a person's intrinsic motivation to perform a task. According to self-perception theory, people pay more attention to the external reward for an activity than to the inherent enjoyment and satisfaction received from the activity itself. The overall effect of offering a reward for a previously unrewarded activity is a shift to extrinsic motivation and the undermining of pre-existing intrinsic motivation. Once rewards are no longer offered, interest in the activity is lost; prior intrinsic motivation does not return, and extrinsic rewards must be continuously offered as motivation to sustain the activity.
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.
According to self-perception theory, a person infers causes about his or her own behavior based on external constraints. The presence of a strong constraint (such as a reward) would lead a person to conclude that he or she is performing the behavior solely for the reward, which shifts the person's motivation from intrinsic to extrinsic.
Cognitive evaluation theory proposes that tangible rewards (like money) are perceived as controlling or coercive. They remove the feeling of self-determination and thus decrease intrinsic motivation. If rewards are unexpected, then the feeling of self-determination is preserved and there is no effect on motivation. On the other hand, informational rewards (like praise) can increase intrinsic motivation by creating a feeling of mastery and self-determination. As a sub-theory of self-determination theory, cognitive evaluation theory explains that intrinsic motivation is maintained or increased when perceived autonomy is preserved or enhanced by rewards or feedback.
The introduction of extrinsic rewards can change the framing of a given task, shifting the motivation from intrinsic to extrinsic. Similar to how Tom Sawyer convinced his friends to whitewash a fence for him by describing the task as a privilege, individuals change their motivations for a task depending on how that task is framed, which is determined by the incentives present. When previously the incentive was only to enjoy the task itself (akin to play), introducing a financial incentive causes the task's participants to shift to a different frame of mind in which they perceive that they are performing the task in order to receive the financial reward instead (akin to work). The market in which such exchanges take place can therefore influence motivations. Moving to a monetary market generally reduces intrinsic motivation.
The overjustification effect is controversial because it challenges previous findings in psychology on the general effectiveness of reinforcement on increasing behavior, and also the widespread practice of using incentives in the classroom. In fact, a 2001 meta-analysis showed that rewards can increase intrinsic motivation for tasks that initially hold little intrinsic interest. Nevertheless, two meta-analyses found that, for high-interest tasks, intrinsic motivation is diminished by expected, tangible rewards in both children and adults, especially when the reward is given for simply performing a task, regardless of the results. Nontangible rewards, such as verbal praise, and unexpected rewards do not undermine intrinsic motivation. In fact, praise may actually increase intrinsic motivation, as long as the praise is interpreted as sincere and a valid signal about the actor's competence.
These conclusions were challenged in a separate meta-analysis which found that tangible rewards offered for outperforming others and for performing uninteresting tasks (in which intrinsic motivation is low) lead to increased intrinsic motivation, and stated that the detrimental effects of rewards on motivation only occur in a specific, restricted set of conditions that could be easily avoided. This set of analyses included both high-interest and low-interest tasks, whereas the original meta-analyses conducted by Deci and colleagues (1999) restricted analyses to tasks in which participants initially had high interest.
A rebuttal defended the original findings, concluding that this analysis by Cameron (2001) was flawed and that Cameron's inclusion of boring tasks in analyzing potential overjustification effects made little theoretical or practical sense. This rebuttal argued that cognitive evaluation theory is the most consistent structure for explaining the effects of rewards on intrinsic motivation, pointing to several other papers that have supported the theory.
Research in this area suggests that parents and educators should rely on intrinsic motivation and preserve feelings of autonomy and competence as much as possible. When the task is unattractive and intrinsic motivation is insufficient (e.g., household chores), then extrinsic rewards are useful to provide incentives for behavior. Student grades may not undermine intrinsic motivation because grades convey information about competence, much like praise.
School programs that provide money or prizes for reading books have been criticized for their potential to reduce intrinsic motivation by overjustification. However, a study of the Pizza Hut program, Book It!, found that participation in the program neither increased nor decreased reading motivation. Although motivating students to read by rewarding them may undermine their interest in reading, it may also encourage the reading skills necessary for developing an interest in reading.
The term gamification refers to the application of game design elements to non-game contexts in order to drive participation, often with the goal of encouraging greater engagement with the non-game context by providing symbolic rewards such as points, badges, or virtual currency. However, a number of academics and other critics have expressed concern that these rewards may backfire via the overjustification effect. Drawing directly on self-determination theory, these critics of gamification express concerns that gamified contexts such as foursquare might provide expected rewards for activities that do not adequately meet self-determination theory’s three innate needs for intrinsic motivation—relatedness, autonomy, and competence—and therefore reduce intrinsic interest in those activities.
Websites that rely on user-generated content sometimes offer monetary rewards for contributions, but these may cause the contributors to succumb to the overjustification effect and stop contributing. For example, Amazon Mechanical Turk allows the creator of a task to offer a monetary reward, but a survey of 431 Mechanical Turk participants showed that they are driven more by intrinsic motivations than a desire for the usually meager monetary compensation. The overjustification effect was also considered in a study on how to maximize contributions when crowdsourcing creative endeavors.
Empirical evidence shows that expected financial rewards "crowd out" intrinsic motivation, while the size of the monetary reward simultaneously provides extrinsic motivation. If the size of the monetary reward is not large enough to compensate for the loss of intrinsic motivation, overall engagement can decline. A survey data-set revealed that small financial payments reduced volunteer hours among Swiss citizens, and that the median financial reward provided to these volunteers caused them to work less than volunteers who were not given any payment.
See also 
- Attribution theory
- Cognitive evaluation theory
- Motivation crowding theory
- Self-determination theory
- Social psychology
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- Deci, E. L. (1995). Why we do what we do: The dynamics of personal autonomy. New York: G.P. Putnam's Sons. ISBN 0-399-14047-6.
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- Deterding, Sebastian; Kenton O'Hara, Miguel Sicart, Dan Dixon, Lennart Nacke (2011). "Gamification: Using game design elements in non-gaming contexts". CHI.
- Groh, Fabian (February 14, 2012). "Gamification: State of the art definition and utilization". Proceedings of the 4th Seminar on Research Trends in Media Informatics.
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- Kaufmann, Nicolas; Schulze, Thimo; Veit, Daniel (August 4, 2011). "More than fun and money: Worker Motivation in Crowdsourcing – A Study on Mechanical Turk". Proceedings of the Seventeenth Americas Conference on Information Systems, Detroit, Michigan.
- Akar, Oguz Ali; van den Ende, Jan (January 20, 2011). "Motivation, Reward Size and Contribution in Idea Crowdsourcing". Dime-Druid Academy Winter Conference 2011.
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Further reading 
- Deci, E.L. (1995). Why we do what we do: The dynamics of personal autonomy. New York: G. P. Putnam's Sons.
- Kohn, A. (2005). Unconditional parenting: Moving from rewards and punishments to love and reason. New York: Atria Books.
- Pink, D.H. (2009). Drive: The surprising truth about what motivates us. Riverhead.