"people who responded to the two ads scored differently on a set of psychological tests. Those who thought that they would be participating in a prison study had significantly higher levels of aggressiveness, authoritarianism, Machiavellianism, narcissism, and social dominance, and they scored lower on measures of empathy and altruism."
http://www.newyorker.com/science/maria-konnikova/the-real-lesson-of-the-stanford-prison-experiment?mbid=social_facebook
http://www.newyorker.com/science/maria-konnikova/the-real-lesson-of-the-stanford-prison-experiment?mbid=social_facebook