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Public Goods Contribution Game

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About This MicroSim

This MicroSim simulates the classic public goods game to demonstrate the free rider problem. You and four AI players each start with $10 per round and choose how much to contribute to a shared public good (a park). All contributions are doubled and then split equally among all five players. The tension is clear: everyone benefits if all contribute, but each individual can earn more by contributing nothing and free-riding on others' contributions. This illustrates why public goods are underprovided by markets without collective action or government intervention.

How to Use

  1. Set your contribution using the "Give" slider (from $0 to $10 per round).
  2. Click "Submit Round" to play one round. Your contribution and the AI players' contributions are pooled, doubled, and divided equally.
  3. Click "Play 5 Rounds" to automatically play five consecutive rounds at your current contribution level.
  4. Observe the results panel on the right showing the total pool, doubled amount, your share, and your payoff. The "What-if" section shows what you would have earned by free-riding ($0 contribution) versus full cooperation.
  5. Track your history in the bar chart below, which shows your payoff for each round. The scoreboard shows cumulative totals for all players.
  6. Click Reset to start a new 10-round game.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://dmccreary.github.io/economics-course/sims/public-goods-game/main.html"
        height="507px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

9-12 (High School Economics)

Duration

10-15 minutes

Prerequisites

  • Understanding of public goods (non-excludable, non-rivalrous)
  • Basic knowledge of incentives and rational self-interest
  • Familiarity with the concept of market failure

Activities

  1. Exploration (5 min): Have students play a full 10-round game first with a contribution of $0 (pure free rider), then reset and play with a contribution of $10 (full cooperator). Compare the total earnings in each case and discuss the results.
  2. Guided Practice (5 min): Ask students to find a contribution level that maximizes their personal payoff. Discuss why the individually rational choice (contribute less) leads to a collectively worse outcome (underfunded park). Connect this to real-world public goods like national defense, street lighting, and clean air.
  3. Assessment (5 min): Students write a response explaining the free rider problem using evidence from the simulation, and propose one mechanism (taxation, social norms, or regulation) that could solve the underprovision of public goods.

Assessment

  • Students can explain the free rider problem and why it leads to underprovision of public goods.
  • Students can identify the tension between individual rationality and collective welfare using payoff data from the game.
  • Students can propose real-world solutions to the free rider problem and evaluate their effectiveness.

References

  1. Public goods game - Wikipedia -- Overview of the game theory model used to study voluntary contributions to public goods.
  2. Free-rider problem - Wikipedia -- Explanation of why individuals have incentives to undercontribute to shared resources.
  3. Public good (economics) - Wikipedia -- Definition and characteristics of public goods, with examples and policy implications.