COVID-19: Early evening curfews and mobility.

During the COVID-19 pandemic, some countries introduced early evening curfews. Several studies try to measure the effectiveness of such measures across different countries, but disentangling competing effects can be elusive. We examined the impact of an early evening curfew on mobility by studying a shift in curfews from 9pm to 6pm in Greece using Google mobility data. We followed a difference-in-differences (DiD) econometric approach, where we compared trends in mobility in residential spaces as well as groceries and pharmacies, before and after the introduction of the 6pm curfew in Attica with trends in three other comparable Regions. We found little or no evidence of an effect of the early curfew on daily mobility relating to groceries and pharmacies, and that an 18.75% reduction in hours where people were allowed to leave home led to a relatively small increase in time spent in residential spaces. This less-than-proportionate reduction in mobility outside the household suggests a possibility that the curfew led to more people coinciding in indoor public spaces, such as grocery shops - which constitutes a contagion risk factor. Results should be treated with caution, especially with regards to the magnitude of any effect, as Google mobility data do not report the time of the day, so the time density of activities cannot be estimated. Lockdowns and other measures are necessary to tackle Covid-19, but it is important to avoid substitution by activities that contribute further to spreading the virus. Interventions should therefore be based on a thorough analysis of human behaviour.