Trust Game n.
Unlike the dictator game, which has no return step, the trust game adds a reciprocity decision, making it a joint measure of trust and trustworthiness rather than pure allocation preference.
also known as investment game
The definition
Trust Game is an experimental economics paradigm in which one participant sends part of an endowment to an anonymous partner, the sent amount is multiplied, and the partner decides how much of it to return. The design isolates trust and reciprocity from altruism, reputation and enforceable contracts, letting researchers measure trusting behaviour using real money rather than surveys.
The mechanism
Berg, Dickhaut and McCabe designed the trust game in 1995, giving one player, the trustor, an initial endowment and letting the trustor send any portion to an anonymous partner, the trustee1. An endowment multiplier of three then triples whatever amount is sent before the trustee decides how much of that increased sum to return, and because the game is played once with no enforceable contract and no chance to build a reputation, the design strips away every incentive to cooperate except trust itself.
Individual differences in trust-game behaviour do not look like noise. Resting-state functional connectivity between specific brain networks, measured before any game is played, predicts how much a given person will send and return, suggesting the behaviour tracks a relatively stable disposition rather than a mood that shifts from one session to the next3.
Sending is not automatic. Imposing a cognitive load on trustors, such as holding a number in working memory while deciding, reduces the amount they send, showing that the decision draws on limited deliberative capacity rather than running as a reflexive default5.
In practice
Consider a freelance graphic designer deciding whether to start a project before or after a new client transfers a deposit.
Worked example
The client offers to pay half upfront and half on delivery, with no contract beyond an email. The designer could demand the full amount before starting, protecting against non-payment but risking the client walking away. Sending nothing forces the client to prove trustworthiness first; starting the work on the promise of a deposit hands over exactly the kind of unenforceable trust the trust game measures in a laboratory.
The freelancer facing that decision is playing an informal version of the trust game, weighing the same trade-off between the amount at risk and the return a trustworthy partner is likely to make.
Why it matters
The trust game matters because it gives a field long dependent on self-report surveys a behavioural, monetary measure of trust and trustworthiness that generalises across settings. A meta-analysis pooling 162 replications and more than 23,000 participants found trustors send an average of 50% of their endowment and trustees return an average of 37%, giving researchers a stable benchmark against which any new claim about trust can be checked2.
That benchmark has already overturned a popular claim. A large, adequately powered registered replication found no effect of a single oxytocin dose on how much trustors sent under standard conditions, undercutting the widely repeated idea that one hormone reliably switches trust on4. The result matters beyond the laboratory: any claim that a supplement, drug or intervention boosts trust needs to be tested against the same benchmark, not asserted from a single small study.
Questions of record
What is the trust game in economics?
It is an experimental design in which one player, the trustor, sends part of an initial endowment to an anonymous partner, the trustee. The sent amount is tripled, and the trustee then decides how much to return, letting researchers observe trust and reciprocity through real money rather than a questionnaire.
How much money do people typically send in a trust game?
Across a meta-analysis of 162 replications covering more than 23,000 participants, trustors sent an average of 50% of their endowment, and trustees returned an average of 37% of what they received. Those figures now serve as the standard benchmark researchers compare new trust-game results against.
Does oxytocin really increase trust?
The popular claim that a single dose of oxytocin boosts trust-game sending has not held up under scrutiny. A large, adequately powered registered replication found no effect of oxytocin on how much trustors sent under standard conditions, which is the kind of result that should carry more weight than the smaller, earlier studies that first popularised the claim.
What is the difference between the trust game and the dictator game?
The dictator game gives one player money to split with a passive recipient who has no choice in the matter, measuring pure allocation preference. The trust game adds a return step: the receiving player, the trustee, decides how much to send back, which turns the exchange into a genuine test of reciprocity rather than one-way giving.