Social distancing during the COVID-19 pandemic will save lives. We tested communication strategies to promote social
distancing via an online experiment (N = 500) commissioned by Ireland’s Department of Health. A control group saw a current
informational poster. Two treatment groups saw similar posters with messages that highlighted: (i) the risk of transmission to
identifiable persons vulnerable to COVID-19; (ii) the exponential nature of transmission. We then measured judgements of
behaviours previously identified by focus groups as “marginal” (meaning that people were not sure whether they were
advisable, such meeting others outdoors, or visiting parents). We recorded intention to undertake behaviours and stated
acceptability of behaviours. Our hypotheses, that both treatments would increase participants’ caution about marginal
behaviours, were preregistered (i.e. lodged with an international organisation for open science before data collection). Results
confirmed the hypotheses. The findings suggest that the thought of infecting vulnerable people or large numbers of people can
motivate social distancing. This has implications for communications strategies. The stud
