The need for comprehensive and representative data collection on populations for epidemiological research has been brought into sharp focus by the COVID-19 pandemic. This has resulted in the generation of many COVID-specific modules within existing cohorts and datasets (e.g. Henderson et al, 2020, Kwong et al, 2020). These datasets are going to be invaluable in understanding the mental health response of individuals to the COVID-19 pandemic. These studies reflect individuals responding under unique circumstances, presenting unique selection effects, which have the capacity to substantially bias results (Griffith et al. 2020). These selection effects are likely to be particularly stark with respect to mental health, which is known to be associated with non-response (Kwong, 2019). The data and analysis will be carried out by GG and DS, and data stored on the University of Bristol RDSF.