The smoking status variable (ie, never, former, current) rather than Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) defined nicotine dependence was selected to assess tobacco use because: (1) the adequacy of the DSM-IV criteria as a valid measure of nicotine dependence remains controversial26 27 and (2) response to the single question on smoking status is easier to elicit in the clinical setting, with more validity, than responses to a multi-item measure of tobacco use for which no consensus, stand-alone instrument yet exists.26 27 To categorise long-term or recent status as never-, former, or current smokers, a change variable was created with the following categories according to their report of smoking at waves 1 and 2: (1) never smoker to never smoker, (2) former smoker to former smoker, (3) current smoker to former smoker, (4) current smoker to current smoker, (5) never smoker to current smoker, (6) former smoker to current smoker and (7) never smoker to former smoker.
