There's been a lot of discussion in economics circles about how economics training makes people more selfish -- in particular, by teaching people "rational choice theory", the cartoon version of which portrays rationality as a matter of always acting in one's perceived (economic) self interest (for example, by defecting in prisoner's dilemma games and offering very little in ultimatum games). Accordingly, the economics literature contains a few much-cited studies that seem to show that economics students behave more selfishly than other students.
However, virtually all the experiments cited in support of this view are flawed in one of two ways. Either they test students on basically the same sorts of games discussed in economics classes, or they rely on self-report of selfishness. Relying on econ-class games makes generalizing the results very problematic. It's no surprise that after a semester of being told by your professor that defecting (basically, ratting on your accomplice to get less prison time) would be the rational thing to do in a prisoner's dilemma game, when that same professor or one of his colleagues gives you a pencil-and-paper version of the prisoner's dilemma, you're more likely to say you'd defect than you would otherwise have been (even with small real stakes). What relationship this has to actually screwing over acquaintances is another question.
Likewise, relying on self-report of selfishness is problematic for all the reasons self-report is usually problematic in the domain of morality, and in this case there's an obvious additional confound: People exposed to rational choice theory might feel less embarrassed to confess their selfish behavior (since it is, after all, rational according to the theory), and so might show up as more selfish on self-report measures even if they actually behave the same as everyone else.
I've found so far only three real-world studies of the relationship between economics training and selfishness, and none suggest that economics training increases selfishness.
(1.) Though I find their study too problematic to rely much on, Yezer et al. (1996) found that envelopes containing money were more likely to be forwarded with the money still in them if they were dropped in economics classes than other classes.
(2.) Frey and Meier (2003) found that economics majors at University of Zurich were less likely than other majors to opt to give to student charities when registering for classes, but that effect held starting with the very first semester (before any exposure to rational choice theory), and the ratio of economics majors to non-economics majors donating remained about the same over time (all groups declined a bit as their education proceeded).
(3.) Studying professional economists, Laband and Beil (1999) found a majority to pay the highest level of dues to the American Economic Association (dues prorated on self-reported income), though they could without detection or punishment have reported lower income and so paid less. Through an analysis of proportion paying dues in each income category vs. proportion in the profession making income in those categories they found similar rates of cheating in self-reported income among sociologists and political scientists.
I see these findings as the flip side of what I've been finding with ethicists: Just as ethical training doesn't seem to increase rates of actual moral behavior much, if at all, so also being bathed in rational choice theory (if, indeed, this is what economics students are mostly taught) doesn't seem to induce real-world selfishness.