Evaluating others' behaviour: a public-good experiment with ex-post communication

The present study investigates the effect of ex-post communication on the voluntary provision of public goods. The experiment consists of two stages. In the first stage, paired subjects play a standard public-good game; in the second, each of them evaluates his or her partner's contribution in the first stage and sends a free-form written message to him or her. The experimental results show that the mere presence of an opportunity for ex-post communication is not enough to promote cooperation. However, once subjects actually receive negative messages, they contribute significantly more in the following round. Positive messages, by contrast, do not have such an effect.