Promises as Commitments

We implement a trust game in which the trustee can write a free-form pre-play message for the trustor. The main twist in our design is that there is a 50% probability that the message is delivered to the trustor and a 50% probability that the message is replaced by an empty sheet. We find that even when messages are not delivered trustees who make a promise are significantly more likely to act trustworthy than those who do not make a promise. This suggests that a promise has a commitment value which is independent of its impact on the trustor. Interestingly, we also find that both trustees who make a promise and those who do not make a promise are more likely to be trustworthy if their message is delivered to the trustor. This means that communication increases trustworthiness irrespective of the content of messages