Our findings revealed some statistically significant non-invariance for FTND items, including CPD, which is often collected and analyzed on its own. However, the effect sizes of the item-level non-invariance accounted for <0.5% of the model variance, indicating that while it is advisable to control for year of birth in analyses using FTND, failure to do so should not greatly alter analytic results, which was confirmed through analyses examining the impact of adjusting for the measurement non-invariance in regression models. In models evaluating the association between FTND and quitting smoking, the odds ratios, and 95% CI estimates were unchanged when controlling for the measurement non-invariance. Moreover, even in genetic analyses where the effects of SNPs often account for small portions of the variance in nicotine dependence (altogether <15%; Hartz, et al., 2017), the measurement non-invariance is likely to have little demonstrable effect, as evidenced by β and 95% CI estimates of the FTND and rs16969968 association being unchanged when controlling for the measurement non-invariance. Therefore, although smoking patterns have changed over time, these changes have not affected the ability of the FTND to assess nicotine dependence.
