Strengths and limitations of the study are noted. An important strength is the concomitance of rigorous methods and materials not found in prior work on the smoking–suicide question—face-to-face interviews, a longitudinal design, a large sample, a validated instrument and a comprehensive range of putative predictors that permitted statistical control of key background factors and comorbidities. A further strength is the use of a simple yet meaningful measure of smoking status (ie, never, former or current smoking) that is easy for a questioner to administer and for the respondent to recall and understand. Even so, study limitations call for cautious interpretation of the findings. The present sample comprised the subgroup (22%) of wave 2 participants (N=34 653) who self-reported low mood during the 3-year interval between the interviews. This selectivity yields findings relevant to mental health settings that are likely to serve persons experiencing mood problems; however, they may not generalise to the rest of the NESARC sample or to the national population. Second, the sample did not include persons who had completed suicide attempts. Using the US rate of 11.1
