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.
This Discussion Paper has been substantially revised and has been published under the title “Why do promises affect trustworthiness, or do they?”, in Experimental Economics, 19(2), 382-393, June 2016. link