What is the cobra effect in simple terms?

It's when a reward meant to shrink a problem ends up making it bigger. The name comes from a story in which paying people for dead cobras led them to start breeding cobras for the cash.

Did the cobra story really happen?

The Indian cobra story is more of a passed-down anecdote than something confirmed by records from the time. But there are historical records of cases with the same structure, such as the 1902 rat-tail bounty in Hanoi.

Cobra Effect

📈 Economics By CampusDown Wiki Editorial Team Last updated October 27, 2026

The cobra effect is the phenomenon in which an incentive introduced to solve a problem prompts strategic responses that make the problem worse. The name comes from a story set in British colonial Delhi: to reduce the number of cobras, authorities paid a bounty for dead ones, so people began breeding cobras, and when the program was scrapped they released their snakes, leaving more cobras than before. The German economist Horst Siebert popularized it with a 2001 book of the same name.

Contents

1. The story and the historical record
2. The structure seen through incentive theory
3. Policy cases and lessons
4. FAQ
5. References

The story and the historical record

The cobra bounty story spread widely after Siebert (2001) used it as a flagship example of misguided economic policy, but it is closer to a received anecdote than a fact confirmed by records from the period. Similar cases, however, are well documented. Drawing on archival sources, Vann (2003) showed that in 1902, when the French colonial authorities in Hanoi paid a bounty for rat tails to cut the rat population, people cut off the tails and released the rats to breed, and some even farmed rats. The sociologist Merton (1936) set out a theory that purposive social action produces unanticipated consequences through ignorance, error and an overriding focus on immediate interests, and the cobra effect can be seen as the special case in which an incentive backfires.

The structure seen through incentive theory

Kerr (1975) pointed to the folly of rewarding A while hoping for B, which is the core structure of the cobra effect: the policy goal was fewer cobras, but rewards were paid per cobra brought in. Holmström and Milgrom's (1991) multitask agency theory showed that strong incentives on measurable tasks lead people to neglect tasks that are hard to measure. Goodhart's law (Goodhart, 1975) and Campbell's law (Campbell, 1979) warned that when an indicator becomes a target, people game it and it loses its original meaning, and the Lucas (1976) critique likewise stressed that when policy changes, people's behavioral rules change too. Gneezy and Rustichini (2000) showed that when Israeli day care centers fined parents for late pickups, lateness actually increased, revealing that monetary incentives can crowd out social norms.

Policy cases and lessons

Davis (2008) showed that when Mexico City restricted driving on certain days based on the last digit of license plates to reduce air pollution, people bought older, more polluting used cars as second vehicles, and air quality did not improve. Hood (2006) found widespread gaming aimed at hitting target numbers in the performance-target management of British public services, and Muller (2018) gathered such cases under the heading of the tyranny of metrics. Gneezy, Meier and Rey-Biel (2011) reviewed from an economic perspective the conditions under which incentives effectively change behavior and those under which they backfire. Along with the Jevons paradox, in which efficiency gains increase consumption, and the Peltzman effect, in which safety rules encourage riskier behavior, the phenomenon teaches that policy design must account for how people adapt.

FAQ

What is the cobra effect in simple terms?: It's when a reward meant to shrink a problem ends up making it bigger. The name comes from a story in which paying people for dead cobras led them to start breeding cobras for the cash.
Did the cobra story really happen?: The Indian cobra story is more of a passed-down anecdote than something confirmed by records from the time. But there are historical records of cases with the same structure, such as the 1902 rat-tail bounty in Hanoi.

Sources reviewed: 2026-10-26

References

Merton, R. K. (1936). The unanticipated consequences of purposive social action. American Sociological Review, 1(6), 894–904.
Kerr, S. (1975). On the folly of rewarding A, while hoping for B. Academy of Management Journal, 18(4), 769–783.
Goodhart, C. A. E. (1975). Problems of monetary management: The U.K. experience. Papers in Monetary Economics (Vol. 1). Sydney: Reserve Bank of Australia.
Campbell, D. T. (1979). Assessing the impact of planned social change. Evaluation and Program Planning, 2(1), 67–90.
Holmström, B., & Milgrom, P. (1991). Multitask principal-agent analyses: Incentive contracts, asset ownership, and job design. Journal of Law, Economics, & Organization, 7(Special Issue), 24–52.
Gneezy, U., & Rustichini, A. (2000). A fine is a price. Journal of Legal Studies, 29(1), 1–17.
Siebert, H. (2001). Der Kobra-Effekt: Wie man Irrwege der Wirtschaftspolitik vermeidet. Stuttgart: Deutsche Verlags-Anstalt.
Vann, M. G. (2003). Of rats, rice, and race: The Great Hanoi Rat Massacre, an episode in French colonial history. French Colonial History, 4, 191–203.
Hood, C. (2006). Gaming in targetworld: The targets approach to managing British public services. Public Administration Review, 66(4), 515–521.
Davis, L. W. (2008). The effect of driving restrictions on air quality in Mexico City. Journal of Political Economy, 116(1), 38–81.
Gneezy, U., Meier, S., & Rey-Biel, P. (2011). When and why incentives (don't) work to modify behavior. Journal of Economic Perspectives, 25(4), 191–210.
Muller, J. Z. (2018). The Tyranny of Metrics. Princeton: Princeton University Press.
Lucas, R. E. (1976). Econometric policy evaluation: A critique. Carnegie-Rochester Conference Series on Public Policy, 1, 19–46.

Reports and materials that use this theory (Korean)

There are no materials dedicated to this theory yet, but you can search related reports in the CampusDown library (Korean).

Find more reports · Search '코브라 효과' on CampusDown →

Goodhart's LawWhat Goodhart's law is, its origin in 1975 U.K. monetary policy, Strathern's popular phrasing, Campbell's law and the Lucas critique, multitask agency theory, health and education cases, and reward-model overoptimization in AI.📈 Economics Campbell's LawWhat Campbell's law is, Donald Campbell's 1976 statement, how it differs from Goodhart's law, cases in high-stakes testing, crime statistics and health targets, the multitask agency model, and ways to limit indicator corruption.👥 Sociology Peltzman EffectWhat the Peltzman effect is: the hypothesis that safety regulation can lead people to take more risks, offsetting expected safety gains; its origin in Peltzman's 1975 study, risk compensation, risk homeostasis theory and the empirical debate.📈 Economics Jevons ParadoxWhat the Jevons paradox is: why improvements in resource efficiency can raise total resource use, its origin in Jevons's 1865 Coal Question, its link to the rebound effect, the Khazzoom–Brookes postulate, empirical estimates and policy debates.📈 Economics Free-Rider ProblemWhat the free-rider problem is: benefiting without paying, non-excludable public goods, Samuelson's theory, Olson's group-size argument and selective incentives, experimental evidence, Ostrom's institutions and applications to firms.📈 Economics

Latest ArticlesView all ›

New guides for college study and assignments (Korean)

This article was last updated on October 27, 2026. It is based on widely recognized original works and textbooks; when citing it in a paper, please check the original sources listed in the references.