Interactive simulator

Behavioral Nudge Simulator

Behavioral economics shows that how choices are framed changes what people choose. This simulator presents a decision — for example, retirement-plan enrollment — under opt-in versus opt-out defaults, and lets you adjust framing, salience, and social-proof messages. Watch participation rates respond even though prices and payoffs never change. In this release this page is powered by the closest available interactive widget; a dedicated widget for this topic is planned.

Prisoner's Dilemma Lab

Edit the payoffs, pick both strategies, find the Nash equilibrium

R — mutual cooperation

T — temptation

S — sucker

P — mutual defection

Payoff matrix — each cell shows (You, Opponent)
	Opp: Cooperate	Opp: Defect
You: Cooperate	(3, 3)	(0, 5)
You: Defect	(5, 0)	(1, 1) ★ NASH EQUILIBRIUM

Your move:

Opponent's move:

You earn 3, opponent earns 3

This is not a Nash equilibrium — at least one player would deviate.

How to read it

A cell is a Nash equilibrium when no player can improve by switching alone. With the classic payoffs (T=5, R=3, P=1, S=0), defecting always pays more no matter what the opponent does — so (Defect, Defect) is the unique equilibrium, even though both players would earn more at (Cooperate, Cooperate).

How to use it

Switch between opt-in and opt-out defaults.
Add a social-proof message and watch participation move.
Compare outcomes while incentives stay constant.

What you will learn

Explain what a nudge is.
Distinguish nudges from mandates and incentives.
Evaluate a nudge on libertarian-paternalist grounds.

Model notes

Participation responses are illustrative, not measured from experiments. Real nudge effects vary by context and population; this tool teaches the mechanism, not any specific result.