Other drug dependence was recorded if participants reported lifetime dependence on any of the following: cocaine (all forms), stimulants, opiates and major painkillers, sedatives, hallucinogens, dissociatives, solvents and inhalants. Participants were classified as meeting lifetime criteria for DSM-IV drug dependence if they reported 3 or more of the 7 DSM-IV symptoms of dependence (American Psychiatric Association, 2000) occurring within the same 12 month period. Self-reported age of onset of dependence was used to create a time varying covariate for other drug dependence. This covariate was only included in the model of progression to the development of dependence.
