Data analyses were conducted in two phases. First, we tested whether the full model provided for a significant increment in the proportion of variance explained in baseline smoking-related characteristics above and beyond either the nicotine-applicable model or the negative-reinforcement model using linear regression analyses. Analyses were conducted as follows: (i) both the nicotine-applicable model and the negative-reinforcement model were estimated; (ii) the remaining DSM-IV items missing from each model were added to the nicotine-applicable model and the negative-reinforcement model; thus, each resulting in the same full model; (iii) the full model was estimated, and the increment in R2 upon the addition of the remaining items to the nicotine-applicable model and the negative-reinforcement model was tested. These analyses represented the tests of concurrent validity of the three models.
