Uncertainty about the impact of social decisions increases prosocial behavior

Uncertainty about how our choices will affect others infuses social life. Past research suggests uncertainty has a negative effect on prosocial behavior by enabling people to adopt self-serving narratives about their actions. We show that uncertainty does not always promote selfishness. We introduce a distinction between two types of uncertainty that have opposite effects on prosocial behavior. Previous work focused on outcome uncertainty: uncertainty about whether or not a decision will lead to a particular outcome. But as soon as people’s decisions might have negative consequences for others, there is also impact uncertainty: uncertainty about how badly others’ well-being will be impacted by the negative outcome. Consistent with past research, we found decreased prosocial behavior under outcome uncertainty. In contrast, prosocial behavior was increased under impact uncertainty in incentivized economic decisions and hypothetical decisions about infectious disease threats. Perceptions of social norms paralleled the behavioral effects. The effect of impact uncertainty on prosocial behavior did not depend on the individuation of others or the mere mention of harm, and was stronger when impact uncertainty was made more salient. Our findings offer insights into communicating uncertainty, especially in contexts where prosocial behavior is paramount, such as responding to infectious disease threats.