Association of sleep with moral severity to accidental harm transgressions: A cross-sectional study.

Based on the assumptions that moral judgement activities require cognitive control, a capacity impaired by low sleep quality or a lack of sleep, several studies have explored the association between sleep and moral judgements. However, even if some studies support the association between sleep and both moral awareness and unethical behaviours, others failed to find a robust association between sleep and moral utilitarianism. In the present well-powered preregistered cross-sectional study, we explored the role of sleep in another class of moral judgement, namely third-party punishment (in which people have to assess the morality of an agent who transgressed a moral rule). Specifically, we targeted the association of sleep with judgements of accidental harm transgressions, which are assumed to be especially cognitively costly. Our main analysis showed no association of overall sleep quality during the past month with moral severity in these transgressions. This result was confirmed for other sleep indexes (sleep quantity in the past month, and sleep quantity and quality in the past night). Lastly, we exhaustively explored the associations of all sleep indexes with all classes of moral judgement (accidental, intentional, attempted transgressions and control scenarios). These additional results revealed associations between sleep and moral severity, but none survived correction for multiple testing. Equivalence tests confirmed that the effect sizes of all these associations were relatively low (|r < 0.25|). We ensured that the lack of robust association between natural sleep and third-party punishment could not be explained by a low quality of the data collected.