摘要：When subjects can make non-binding announcements of possible contributions to a
public good numerically, there is no effect on average level of contributions in a
public goods experiment relative to play without announcements. But a detailed
analysis of this experiment shows that pre-play announcements increased the variance
of achieved cooperation among groups, leading both to more highly cooperative
groups and to more thoroughly uncooperative groups than in a treatment without
announcements. We also add a treatment in which subjects can select a statement of
(non-binding) “promise” to contribute a certain amount and we find that even though
subjects were instructed that promise statements were not binding, the ability to issue
them significantly increased both contributions and earnings in a treatment that
includes costly punishment opportunities, although not in a treatment without
punishment.
