Which is the Fair Sex? Gender Differences in Altruism
By James Andreoni and Lise Vesterlund

1.  Introduction

     Recent experimental evidence suggests that individuals may have a taste for fair or
altruistic outcomes.  For instance, people often do not free ride in public goods games, 
they tend to make generous offers and reject selfish offers in ultimatum games, and in dictator 
games many subjects don't keep the whole pie.  In addition, there is a great deal of variation 
across individuals in the degree of altruistic behavior, ranging from extremely generous to perfectly
selfish.  There is now a great deal of research directed at explaining fairness in experiments.  
     These findings raise the the natural question of whether there is something systematic
about individual differences in altruism.  These effects may help to inform theories of altruism. 
However, a more immediate concern is that if observable factors about subjects can predict their
degree of altruism, then these factors should be reported by experimenters and accounted for in
the experimental design. 
     Perhaps the most obvious systematic predictor to examine is gender.  Many people have
the instinctive feeling that women are more altruistic than men.  Economists who have looked at
this issue, however, have found conflicting results.  In public goods games, Brown-Kruse and
Hummels (1993) found male groups to be more cooperative than female groups, while Nowell
and Tinkler (1994) found female groups to be more cooperative.  In duopoly games Mason,
Phillips and Redington (1991) found no gender difference.  Looking at ultimatum games, Eckel
and Grossman (1994) found men and women to be no different in the offers they make, but
found women more willing to accept unfair offers than men.  Bolton and Katok (1995)
examined three different versions of dictator games and found no male-female differences in any
version of the game.  Psychologists, too, have found varying results on the question gender
differences in altruism.
     This paper reopens the question of gender differences in altruism.  Rather than simply
looking at mean behavior, we also examine the distribution of behavior.  Our results indicate that
the question "which is the fair sex?" has a complicated answer---sometimes women can appear
more altruistic and sometimes less.  Stated differently, we find that the "demand curves for
altruism" cross.  At high prices of altruism women demand more, at low prices men demand
more, and at prices in between men and women are equally altruistic.  Moreover, men seem to be
more extreme.  They are more likely to be both perfectly selfish and perfectly selfless, whereas
women tend to be "equalitarians" who prefer to share evenly.  Hence, our results not only explain
male-female differences, but have the potential to unify a large number of apparently
contradictory findings by other researchers.