Secular trends in smoking might produce measurement non-invariance in longitudinal studies and studies that incorporate cross-sectional data collected at different times across multiple samples if the salience of dependence symptoms were affected across different birth cohorts. Smoking prevalence was relatively low in the U.S. before 1939 but increased up until the 1960s, when almost half of adults smoked. The 1964 Surgeon General’s report (U.S. Surgeon General’s Advisory Committee on Smoking and Health) marked another turning point, and smoking prevalence has fallen since (Figure S1)1 (U.S. Department of Health Human Services, 2014). A concomitant evolution in the social stigma and legal context of smoking have also affected smoking behaviors that are key indicators of dependence in the FTND (e.g., more difficulty refraining from smoking, fewer cigarettes per day [CPD] because smoking is forbidden in many public places), potentially making them more salient indicators of nicotine dependence.
