Emmons, R.A., & McCullough, M.E., (2003). Counting Blessings Versus Burdens: An Experimental Investigation of Gratitude and Subjective Well Being in Daily Life. Journal of Personality and Social Psychology, 54 (1), 377-389. 3. Emmons, R.A. (2007). Thanks! How the Science of Gratitude Can Make You Happier, Houghton Mifflin Company. 4. Dunn, E. & Norton, M. (2013). Happy Money: The Science of Smarter Spending. New York: Free Press Simon & Schuster. 5. Falk, A. & Fischbacher, U. (2006). A Theory of Reciprocity. Games and Economic Behavior, 54 (2), 293-315. 6. Seligman, M.E.P., Steen, T.A., Park, N.P., & Peterson, C. (2005). Positive psychology progress: Empirical validation of interventions. American Psychologist, 60, 410-421. 7. Seligman, M.E.P. (2002). Authentic Happiness: Using the New Positive Psychology to Realize Your Potential for Lasting Fulfillment, New York: Free Press Simon & Schuster.