Table 1

Details of the models

Models	Structure	Variables	Note
Model 1	Multilevel random intercept model (logistic regression)	Random effect variable: DHB	All model terms had Pr(> χ²) value <0.001
Model 1	Multilevel random intercept model (logistic regression)	Fixed effect variables: age, ethnicity, sex, deprivation, rurality, finance and year-window (stepwise)	All model terms had Pr(> χ²) value <0.001
Model 2	Fixed effect multiple logistic regression model	Age, DHB, ethnicity, sex, deprivation, rurality, year-window and finance (orderly)	As above
Model 3	Fixed effect multiple logistic regression model with interaction	Model 2 variables plus DHB-year interaction term	all model terms had Pr(>χ²) value <0.001, and all VIFs including that for the interaction terms were less than five except for finance variable (VIF=5.06)