Schroeder, D. A., & Penner, L. A. (1995). The psychology of helping and altruism: Problems and puzzles. McGraw-Hill.

Schroeder, David A., and Louis A. Penner. The Psychology of Helping and Altruism: Problems and Puzzles. New York: McGraw-Hill, 1995.

Schroeder, David A., and Louis A. Penner. The Psychology of Helping and Altruism: Problems and Puzzles. McGraw-Hill, 1995.