Andreoni, J., Dept. of Economics, University of California at San Diego, 9500 Gillman Drive, San Diego, CA 94305-6072, United States, NBER, United States; Bernheim, B.D., NBER, United States, Dept. of Economics, Stanford University, Stanford, CA 94305-6072, United States | Social image and the 50-50 norm: A theoretical and experimental analysis of audience effects | Econometrica | 2009