Models | Structure | Variables | Note |

Model 1 | Multilevel random intercept model (logistic regression) | Random effect variable: DHB | All model terms had Pr(> χ^{2}) value <0.001 |

Fixed effect variables: age, ethnicity, sex, deprivation, rurality, finance and year-window (stepwise) | |||

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(>χ^{2}) value <0.001, and all VIFs including that for the interaction terms were less than five except for finance variable (VIF=5.06) |

DHB, District Health Board; VIF, Variance Inflation Factor.