The investigators will estimate the effects of smoking cessation therapies within sub-groups defined by IMD level both at the individual and practice level using the three methods described above, multivariable-adjusted Cox regression, propensity score regression and instrumental variable analysis. The cohort of patients will be defined as described above. The investigators will report these associations adjusted for basic confounders (age and gender), and results adjusted for all measured covariates described above. Analyses will account for clustering of patients by GP practice.