One limitation of our study is that the national survey data (available from the UK Census and the HSE) were presented in prespecified age groups, thereby restricting the comparisons that could be performed. For the majority of characteristics, comparable national survey data were available only for England, although only 11% of participants were recruited in Wales and Scotland and the distributions of most characteristics were similar across the 3 countries. It is also possible that differences in the wording of questions, answer choices, and data collection methods might have influenced the comparability of certain characteristics between the national surveys and the UK Biobank cohort. For example, the HSE consisted primarily of a verbal interview that enabled the interviewer to probe the participant for further information, whereas data on all of the characteristics of UK Biobank participants presented here were collected via a touchscreen questionnaire, with the exception of information on self-reported health conditions, which was collected through a verbal interview with a trained nurse.
