  In this paper we investigate the effect of moral suasion on ingroup
favouritism. We report a well-powered, pre-registered, two-stage 2x2
mixed-design experiment. In the first stage, groups are formed on the basis of
how participants answer to a set of questions, concerning non-morally relevant
issues in one treatment (assorting on non-moral preferences), and morally
relevant issues in another treatment (assorting on moral preferences). In the
second stage, participants choose how to split a given amount of money between
participants of their own group and participants of the other group, first in
the baseline setting and then in a setting where they are told to do what they
believe to be morally right (moral suasion). Our main results are: (i) in the
baseline, participants tend to favour their own group to a greater extent when
groups are assorted according to moral preferences, compared to when they are
assorted according to non-moral preferences; (ii) the net effect of moral
suasion is to decrease ingroup favouritism, but there is also a non-negligible
proportion of participants for whom moral suasion increases ingroup
favouritism; (iii) the effect of moral suasion is substantially stable across
group assorting and four pre-registered individual characteristics (gender,
political orientation, religiosity, pro-life vs pro-choice ethical
convictions).
