Entry or exit? The effect of voluntary participation on cooperation

We study the effects of voluntary participation on public good provision. Voluntary participation may foster cooperation through two mechanisms: an entry mechanism, which leads to assortative selection of interaction partners, or an exit mechanism, whereby the opportunity to leave the partnership can be used as a means to resist exploitation by free-riders. We examine the relative effectiveness of these two mechanisms in a one-shot, two-person public goods game experiment. We find that voluntary participation has a positive effect on public good provision through the exit mechanism, but we do not find evidence of a positive effect of entry. Assortative selection of interaction partners seems to play a minor role in our setting, whereas the threat of costly exit is a powerful force to discipline free-riding.