Piff, Paul K.; Kraus, Michael W.; Côté, Stéphane; Cheng, Bonnie Hayden; Keltner, Dacher (November 2010). "Having less, giving more: The influence of social class on prosocial behavior". Journal of Personality and Social Psychology. 99 (5): 771–784. doi:10.1037/a0020092. PMID20649364.
Piff, Paul K.; Kraus, Michael W.; Côté, Stéphane; Cheng, Bonnie Hayden; Keltner, Dacher (November 2010). "Having less, giving more: The influence of social class on prosocial behavior". Journal of Personality and Social Psychology. 99 (5): 771–784. doi:10.1037/a0020092. PMID20649364.