Prevolio
Game theoryClassroom · multi-user

Trust Game — Trust & Reciprocity

Paired up, a Trustor sends some of 100 points, it triples on the way, and the Trustee chooses how much to send back. See how trust creates value and reciprocity sustains it.

You’ll learn: See why people send and reciprocate even when self-interest predicts sending nothing — and how trust unlocks a surplus that benefits both sides.

Teacher guide

Students will learn to

  • Experience both sides of a trust exchange: deciding how much to risk, and how much to repay.
  • Contrast the game-theory prediction (send nothing, return nothing) with what real people do.
  • Connect the multiplier to the surplus that trust creates, and returns to reciprocity and reputation.

Before the session — ask

  • If sending money to a stranger tripled it, but they decided how much to send back, how much would you send?
  • What would a purely self-interested Trustee return — and knowing that, what should a self-interested Trustor send?

After the session — discuss

  • How much did Trustors send on average, and how much did Trustees give back?
  • Did pairs that trusted more end up better or worse off than the 'send nothing' prediction?
  • Where in real life — lending, charity, business deals — does this same trust-and-repay dynamic show up?

Timing

  • Briefing & pairing3–5 min
  • Send & return4–6 min
  • Reveal & discussion8–10 min

Run it with your class

Students join with a code or QR — no account needed. Teachers start a session from the dashboard.

Join with a codeFor teachers

What is the trust game?

The trust game shows how trust creates value and reciprocity sustains it. A Trustor starts with a sum — say 100 points — and chooses how much to send to a Trustee. Whatever is sent is multiplied on the way (often tripled), so trust literally creates a surplus: the more that is sent, the larger the pie. The Trustee then decides how much of that enlarged amount to send back. Pure self-interest makes a bleak prediction: the Trustee, having no obligation, keeps everything, so the Trustor — anticipating this — should send nothing, and the valuable surplus is never created. In practice, Trustors send substantial amounts and Trustees return meaningful shares, because reciprocity — the impulse to repay trust with trustworthiness — overrides narrow self-interest. This mutual behaviour unlocks the cooperation surplus that the self-interested equilibrium destroys. The trust game is the classic laboratory measure of social capital: it captures why economies built on trust and reciprocated cooperation are more productive than those where everyone assumes the worst and, defensively, sends nothing.

How the simulation shows it

Paired up, a Trustor sends part of 100 points, the amount triples on the way, and the Trustee chooses how much to send back. Playing either role yourself shows the surplus trust creates — and how reciprocity, not obligation, is what makes sending money pay off for both sides.

Common misconceptions

Frequently asked questions

What is the trust game?
An experiment where a Trustor sends part of a sum to a Trustee; the transfer is multiplied (often tripled), and the Trustee decides how much to return. It measures trust and reciprocity.
What does self-interest predict?
That the Trustee keeps everything, so the Trustor, foreseeing this, sends nothing — and the multiplied surplus is never created. Real players depart from this and both gain.
Why does the transfer get multiplied?
To show that trust creates value: sending money enlarges the total pie, so cooperation produces a surplus that wouldn't exist if the Trustor kept everything.
Why do Trustees send money back?
Because of reciprocity — the impulse to repay trust with trustworthiness. Though nothing forces them to, most return a meaningful share, sustaining the cooperation.
What is social capital?
The trust and norms of reciprocity that let people cooperate productively. The trust game is the classic lab measure of it, showing why high-trust economies outperform suspicious ones.

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