Demographic information available included socio‐economic deprivation measured using the Scottish Index of Multiple Deprivation (SIMD) 2009 matched to each participant's postcode (The Scottish Government 2009). SIMD is not a direct measure of an individual's socio‐economic status, but is a ranking for their local area (6505 areas in total with an area population mean of ∼800). It is derived from data on employment, income, health, education, housing, crime and access to services. SIMD is a rank number from 1 to 6505 and the lower the number the more socially deprived the geographical region. Each participant self‐completed a pre‐clinic questionnaire, which included information on their education by asking, ‘how many years altogether did you attend school/study full‐time?’
