Effort-based decision making in joint action: Evidence of a sense of fairness

As humans, we are unique with respect to the flexibility and scope of our cooperative behavior. In recent years, considerable research has been devoted to investigating the psychological mechanisms which support this. One key finding is that people frequently calibrate their effort level to match a cooperation partner's effort costs - although little is known about exactly why they do so. We hypothesized that people calibrate with the ultimate goal of attracting and keeping good collaboration partners, with the proximal psychological motive being a preference for fairness. Across four lab-based, pre-registered experiments (N = 142), we found support for these hypotheses, and distinguished them from plausible alternative explanations, such as the conjecture that people may use their partner's effort costs as information to infer the value of opportunities afforded by their environment, and the conjecture that people may calibrate their effort investment in order to appear competent. Statement of relevance: As humans, we have unique skills and motivations for acting together. Crucially, acting together requires effort and a growing body of empirical work on cooperation and joint action suggests that people calibrate their effort level to match that of a partner's effort costs - although little is known about the mechanisms leading them to do so. Our findings show that people calibrate their effort investment in joint action with the ultimate goal of attracting and keeping good collaboration partners and that the psychological mechanism that drives them to do so is a preference for fairness. These findings provide a valuable addition to existing research on the sense of fairness, providing evidence that the sense of fairness leads people not only to distribute resources according to individual effort costs but to distribute effort costs according to the expected reward distribution as well.