Observed and self-reported COVID-19 health protection behaviours on a university campus and the impact of a single simple intervention.

During the COVID-19 pandemic, most data on adherence to health protective behaviours were collected via a self-report. We quantified the discrepancy between self-report data and discretely observed behaviour in a sample of university staff and students. We assessed the prevalence of cleaning hands, wearing a face-covering and maintaining distance from others. We also tested whether additional signage reminding people that these behaviours were mandatory improved observed adherence. Prevalence estimates based on self-report were higher than those based on observations. Signage was associated with improvements for observed behaviours (all χ2 ≥ 6.0, P < 0.05). We caution that self-reported data can produce misleading adherence rates.