We first evaluated suicide rates by smoking status using a competing risk model. Because smoking causes diseases that may cause a cohort member to die before she/he might have died by suicide, we used competing-risks regression models in the survival data analysis instead of Cox regression to investigate the effect of smoking status on risk of death by suicide (Lau et al. 2009; Haller et al. 2013). Mortality not due to suicide was defined as the competing risk and we modeled the subdistribution hazard using Stata's stcrreg procedure. We tested the assumption of proportionality behind competing-risk regression by a covariate × time interaction. Data were censored by date of emigration or end of follow-up (31 December 2011). We then evaluated whether this association remained after excluding persons with major psychiatric or somatic illness. In models excluding persons with major psychiatric or somatic illness, we then evaluated the association between smoking behavior and suicide in an age-adjusted model controlling for factors that may be independently related to suicide. We planned to retain age, sex, LSS scores, sedative–hypnotic medication use, excess daily alcohol use and binge alcohol use in final models. Other covariates were retained if significantly associated with suicide.
