*2.4. Additional Covariates*

Demographic factors including age, categorised as young adult (18–35 years), middle-age (36–50 years) and older-age (>50 years), and sex of the household reference person were self-reported. Additionally, two indicators of socioeconomic status were patterned by both exposure and outcome: educational attainment categorised as 'None, GCSE or equivalent (≤11 years)', 'A-level (12–13 years)', 'Vocational qualifications (12–13 years)', 'Degree or higher (>13 years)' or 'Missing', and equivalised household income categorised as '£14,999 or below', '£15,000–£24,999', '£25,000–£34,999', '£35,000–£49,999', '£50,000 and above' or 'Missing'. Missing covariates were examined across all exposure variables, with no significant differences in percentages across exposure levels found. As a

result, we included cases with missing covariate data in appropriate models to improve estimates and avoid case deletion (i.e., the missing indicator approach) [38].
