Demographic and clinical characteristics of participants.

p-values are calculated using logistic regression and adjusted for age and gender, with the exception for age, which was calculated using linear regression.‡ Combined p-value from likelihood ratio-test.† P-value for trend.* We merged “very wealthy” and “wealthy” and “very poor” and “poor” because of small numbers at the extremes of the distribution, to create three levels of socio-economic status measure to facilitate data modelling.Demographic and clinical characteristics of participants.