RESUMEN
The aim of this study was to find out if gratitude can increase positive affectivity, happiness and optimism in Iranians with low positive affectivity. In this quasi-experimental study, 636 students of three Iranian Universities [Shahed, Vliasr, and University of Sience and Culture] were chosen using pretest-posttest method. Then 96 low positive affect subjects were chosen. Finally, 62 subjects completed satisfaction form and were assigned randomly into seven groups [Gratitude and Neutral Strategies based on the Emmons, Seligman and Verbal-Action patterns, and a Control group], and received separate instructions in specific envelopes. The data required were collected Positive And Negative Affect Scale [PANAS], Oxford Happiness Questionnaire [OHQ], and Life Orientation Test [LOT]. Then the data of 50 participants were analyzed with Kruskal-Wallis and Mann-Whitney U statistical methods. The results showed significant increase in positive affects by Seligman and V-A strategies [p=0.20], and increase in happiness by Emmons, Seligman and V-A strategies [p=0.04]. The results confirmed the effect of the above three training strategies on the expansion of positive affectivity and happiness