Three regression models were examined: (i) the ‘nicotine-applicable’ model suggested by Hughes [9], consisting of withdrawal, difficulty controlling use and use despite harm as the independent variables; (ii) the ‘negative-reinforcement’ model, consisting of tolerance and withdrawal as the independent variables; and (iii) the ‘full’ model, containing each of the seven DSM-IV criteria as the independent variables. In each model, each of the criteria were coded as 0 = ‘absent, ’ 1 = ‘present.’ Both the nicotine-applicable model and the negative-reinforcement model were nested in the full model.
