Are nurses more altruistic than real state brokers?

This new paper by Jacobsen et al. (Journal of Economic Physiology, October 2011) examines if nurses are more altruistic than real state brokers (although the subjects are students, not practitioners):

We report results from a dictator game experiment with nurse students and real estate broker students as dictators, and Amnesty International as the recipient. Although brokers contributed substantial amounts, nurses contributed significantly more, on average 76 percent of their endowment. In a second part, subjects chose between a certain repetition of the experiment and a 50-50 chance of costly exit. About one third of the brokers and half of the nurses chose the exit option. While generosity was indeed higher among nurses, even when taking exits into account, the difference cannot readily be attributed to different degrees of altruism.

The authors claim that nurses' higher contributions might be due to a higher sense of duty in terms of contribution of their endowment.