Happiness, cooperation and language

According to existing research across several disciplines (management, psychology, economics and neuroscience), positive mood can have positive effects, engendering more altruistic, open and helpful behaviour, but can also work through a more negative channel by inducing inward-orientation, assertiveness, and reduced use of information. This leaves the impact on cooperation in interactive and strategic situations unclear. We find evidence from 490 participants in a laboratory experiment suggesting that participants in an induced positive mood cooperate less in a repeated Prisoner’s Dilemma than participants in a neutral setting. This is robust to the number of repetitions or the inclusion of pre-play communication. In order to understand why positive mood might damage the propensity to cooperate, we conduct a language analysis of the pre-play communication between players. This analysis indicates that subjects in a more positive mood use more inward-oriented and more negative language