Social Cognition
Repeated Prisoner's Dilemma
Also called: prisoner's dilemma game, iterated prisoner's dilemma
Measure cooperation over time: participants choose A or B in each round against one programmed partner, scored by how often they cooperate and how they answer the partner's choices.
3-5 minUntimed
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- Papers, 2021 to 2025
- 865
- Evidence grade
- C
- Registered clinical studies
- 3
What it measures
Measures cooperation over time: in repeated rounds, the participant and a programmed partner each choose to cooperate or defect, where defecting pays more in any one round but mutual cooperation pays more than mutual defection.
Constructs
- Cooperation
- Reciprocity
- Social preferences
- Social decision making
Research uses
- Behavioral economics research
- Cooperation and reciprocity studies
- Social decision-making research in clinical groups
- Within-study group comparison
How the paradigm works
The Repeated Prisoner's Dilemma measures cooperation over time. In each round the participant and a partner each choose one of two options at the same time. If both cooperate, each gets 3 points; if both defect, each gets 1; if one defects while the other cooperates, the defector gets 5 and the cooperator nothing. Defecting pays more in any single round, but mutual cooperation pays more than mutual defection, so each round sets a short-term gain against cooperation. The partner is a computer program that follows set rules, and by default the instructions say so.
More about the paradigm
The task follows the iterated game of Axelrod and Hamilton (1981), with Axelrod's points of 5, 3, 1 and 0. The participant plays 20 rounds as standard against one partner that plays tit for tat: it cooperates in the first round, then repeats the participant's choice from the round before. The number of rounds is not shown, so no round is known to be the last. The options are labelled A and B, and which letter is cooperation is drawn from the session's seed. A comprehension question with feedback comes first, and both choices and the points show after each round. Researchers can set 5 to 50 rounds, show the number of rounds, choose a partner that always cooperates, always defects or chooses at random, use a neutral partner wording, and choose the payment line.
Scores
- Cooperation Rate%
- Share of rounds in which the participant cooperated.
- Higher means more cooperation
- First-Round Cooperation0/1
- 1 when the participant cooperated in the first round, 0 when not.
- Informational
- Cooperation After Partner Cooperated%
- Share of rounds after the partner cooperated in which the participant cooperated.
- Higher means cooperation was returned more often
- Cooperation After Partner Defected%
- Share of rounds after the partner defected in which the participant cooperated.
- Higher means more cooperation after a defection
- Total Pointspoints
- Points the participant earned over all rounds.
- Informational
- Comprehension Check%
- Share of the comprehension questions answered correctly.
- 1 supports interpretation
Use and evidence
865 papers from 2021 to 2025 name this task in their title or abstract, down 2% compared with 2016 to 2020. That ranks it 30 of 395 test families in our census. See the counts for every test.
Show the numbers
| Year | Papers |
|---|---|
| 2025 | 172 |
| 2024 | 184 |
| 2023 | 177 |
| 2022 | 154 |
| 2021 | 178 |
| 2020 | 173 |
| 2019 | 171 |
| 2018 | 183 |
| 2017 | 172 |
| 2016 | 188 |
| 2015 | 199 |
| 2014 | 185 |
| 2013 | 213 |
| 2012 | 186 |
| 2011 | 200 |
| 2010 | 179 |
| 2009 | 183 |
| 2008 | 132 |
| 2007 | 132 |
| 2006 | 143 |
| 2005 | 111 |
| 2004 | 91 |
| 2003 | 69 |
| 2002 | 91 |
| 2001 | 66 |
| 2000 | 73 |
Use grade B
300 to 999 papers from 2021 to 2025.
Evidence grade C
At least 2 test-retest papers, 30 reliability or validity papers or 3 registered clinical studies.
- Papers on test-retest reliability
- 0
- Papers on reliability or validity
- 68
- Registered clinical studies using it as an outcome
- 3
Note on the counts: includes theory papers.
How the grades work
Use: A is 1,000 or more papers from 2021 to 2025, B 300 to 999, C 100 to 299, D 30 to 99 and E fewer than 30. Evidence: A means at least 25 papers report its test-retest reliability and at least 25 registered clinical studies use it as an outcome; B, at least 8 test-retest papers, and either 5 registered clinical studies or 150 reliability or validity papers; C, at least 2 test-retest papers, 30 reliability or validity papers or 3 registered clinical studies; D, little published measurement evidence found. The counts measure use. They include every paper that names the task in its title or abstract. Grades describe the published research on this task, not ConductCognition's version of it.
Source: ConductCognition test census 0.14.0, counted 31 October 2026 from OpenAlex and ClinicalTrials.gov.
Task design
The trial sequence as the test runs in ConductCognition.
- Partner
- One computer program that follows set rules, for the whole game. The standard instructions say so; a neutral wording says only "your partner".
- Points
- Both cooperate: 3 each. Both defect: 1 each. One defects: 5 for the defector and 0 for the cooperator.
- Options
- A and B, chosen at the same time. Which letter is cooperation is drawn from the session's seed and saved.
- Rounds
- 20 (standard; 5 to 50) against the same partner. The number is not shown unless a setting shows it.
- Partner rule
- Tit for tat (standard): cooperates in round 1, then repeats the participant's choice from the round before. Or always cooperate, always defect, or random with a 50% chance of cooperating in each round.
- Outcome
- Both choices and the points show for 2,000 ms after each round.
- Check
- One question with feedback before the first round: the points for an outcome drawn from the seed.
- Money
- Points are hypothetical by default; a setting changes the instruction line to say the study pays.
Axelrod and Hamilton studied strategies for the repeated game in a computer tournament. Here a participant plays one programmed partner for a set number of rounds, not shown by default, and the points are hypothetical unless the study pays.
Quality checks
Each session is marked valid, needs review or invalid, with the reason, before you see its scores.
Scored rows: the scored run's choices in each round. No choice is correct, so accuracy is not judged against chance, and cooperating or defecting in every round is accepted. A wrong comprehension answer is flagged for review. Choices under 200 ms on at least half the rounds invalidate.
Why these rules
There is no correct option to compare with chance, so accuracy is not judged against chance. Cooperating in every round, or defecting in every round, is a strategy, so repeated choices are not checked. A participant who misreads the points may choose the opposite of what they intend, so a wrong comprehension answer is flagged for review and never invalidates. An answer under 200 ms is faster than a simple visual reaction, so it cannot reflect the item. Following response-time effort screening for untimed tests (Wise and Kong 2005), the session is invalid only when at least half the answers are that fast.
No percentile. Scores and quality flags only.
Running this test
Settings you can change
| Setting | Standard | Allowed |
|---|---|---|
| Partner strategy | Tit for tat (standard) | Tit for tat (standard), Always cooperate, Always defect, Random: 50% chance of cooperating each round |
| Rounds | 20 | 5 to 50 |
| Number of rounds shown | Off | On or off |
| Partner wording | A computer program (standard) | A computer program (standard), Neutral: your partner |
| Payment line | Hypothetical points (standard) | Hypothetical points (standard), The study pays for points |
Yearly plans can change settings within these limits. Free and pay-as-you-go studies use the standard settings.
Need a setting this test does not have?
Devices and languages
- Untimed test: runs on desktops, laptops, tablets and phones. Participant devices
- Languages: English, Spanish, French, German, Italian, Portuguese (Brazil), Chinese (Simplified) and Japanese.
- Available on: Every plan, including the free plan.
- No percentile. Scores and quality flags only. How norms work
- Recruiting online? See the setup guides for Prolific, Sona Systems, CloudResearch Connect and Qualtrics.
Cite and describe
Participants completed the Repeated Prisoner's Dilemma task in a web browser (ConductCognition task version 1.0.0, scoring version 1.0.0; Axelrod R, Hamilton WD, 1981), with the standard settings (partner strategy: Tit for tat; rounds: 20; number of rounds shown: Off; partner wording: A computer program; payment line: Hypothetical points). The main score was cooperation rate (share of rounds in which the participant cooperated).
ConductCognition versions: task version 1.0.0, scoring version 1.0.0. Every export records the versions each session used, for a methods section.
- Axelrod, R., & Hamilton, W. D. (1981). The evolution of cooperation. Science, 211(4489), 1390-1396. https://doi.org/10.1126/science.7466396
- Axelrod, R. (1980). Effective choice in the prisoner's dilemma. Journal of Conflict Resolution, 24(1), 3-25. https://doi.org/10.1177/002200278002400101The computer tournament for the repeated game.
- Rilling, J. K., Gutman, D. A., Zeh, T. R., Pagnoni, G., Berns, G. S., & Kilts, C. D. (2002). A neural basis for social cooperation. Neuron, 35(2), 395-405. https://doi.org/10.1016/S0896-6273(02)00755-9Mutual cooperation and reward-related brain activity.
- Dal Bó, P., & Fréchette, G. R. (2011). The evolution of cooperation in infinitely repeated games: Experimental evidence. American Economic Review, 101(1), 411-429. https://doi.org/10.1257/aer.101.1.411Cooperation in repeated games in the laboratory.
Source papers
- Axelrod and Hamilton (1981): the iterated prisoner's dilemma and the points used here. Dal Bó and Fréchette (2011): cooperation in repeated games in the laboratory.Paradigm source, Adults
Questions
How long does the Repeated Prisoner's Dilemma take?
About 3 to 5 minutes, as listed in the test library.
What device does a participant need?
Untimed test: runs on desktops, laptops, tablets and phones. The browser must be Chrome, Edge, Firefox or Safari.
What scores does it produce?
Cooperation Rate, First-Round Cooperation, Cooperation After Partner Cooperated, Cooperation After Partner Defected, Total Points and Comprehension Check. Each session is also marked valid, needs review or invalid, with the reason.
How widely is the Repeated Prisoner's Dilemma used in research?
865 papers from 2021 to 2025 name it in their title or abstract, down 2% compared with 2016 to 2020. That ranks it 30 of 395 test families in the ConductCognition test census (use grade B). Source: ConductCognition test census 0.14.0, counted 31 October 2026 from OpenAlex and ClinicalTrials.gov.
How much reliability evidence does the Repeated Prisoner's Dilemma have?
In the published research, 0 papers report its test-retest reliability and 3 registered clinical studies use it as an outcome (evidence grade C in the ConductCognition test census).
Does it report a percentile?
No. Scores and quality flags only.
Which settings can a researcher change?
Partner strategy (Tit for tat (standard), Always cooperate, Always defect, Random: 50% chance of cooperating each round), rounds (5 to 50), number of rounds shown (On or off), partner wording (A computer program (standard), Neutral: your partner) and payment line (Hypothetical points (standard), The study pays for points). Settings can be changed on yearly plans; free and pay-as-you-go studies use the standard settings.
Which languages can participants use?
Participants can take this test in English, Spanish, French, German, Italian, Portuguese (Brazil), Chinese (Simplified) and Japanese. English is on every plan, and the other languages come with yearly plans. Have a native speaker read the machine-translated text before launch.
Is this a clinical test?
No. ConductCognition is for research use only. It runs, scores and exports the test; clinical interpretation is outside the platform.
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