Person-years of follow-up were calculated from the date of return of the baseline questionnaire (1986 for HPFS, 1976 for NHS, and 1989 for NHS II) to the earliest of: date of death from suicide or another cause; end of follow-up (January 1, 2008 for HPFS, June 30, 2008 for NHS and, June 30, 2007 for NHS II); or return date of the last questionnaire received during follow-up. Cox proportional hazards models, stratified on age in months and questionnaire cycle, were used to estimate relative risks (RRs) and 95% confidence intervals (CIs). Linear trends were tested by modeling medians of categories of exposure. Analyses were performed separately in each cohort and cohort-specific estimates were pooled using random-effect summaries.
