Sample size bias in the empirical assessment of the acute risks associated with daylight saving time transitions

The assessment of the acute impact of daylight saving time (DST) transitions is a question of great interest for an understanding of the benefits and inconveniences of a practice that is now under public scrutiny in Europe and America. Here, we report a thorough analysis of a record of 13 well-known research studies that reported increased risks associated with DST transitions in health issues - acute myocardial infarction, ischemic strokes and trauma admissions - and in societal issues - accidents, traffic accidents and fatal motor vehicle accidents. We found that five increase of the risks suffices to understand the reported increased risks associated with the spring transition. Reported values above this threshold are impacted by the sample size of the study. In the case of the autumn transition, no increase in the risks is found.