What is the evidence for hardening in the cigarette smoking population? Trends in nicotine dependence in the US, 2002-2012

Background: It is unclear whether declines in cigarette smoking in the U.S. have resulted in a hardened population of "hardcore" smokers. We studied changes in nicotine dependence severity from 2002 to 2012, using data from the National Survey on Drug Use and Health. Methods: We used generalized non-linear factor analysis to examine whether individual Nicotine Dependence Syndrome Scale (NDSS) items functioned differently over time, and whether average NDSS scores changed in a sample of 130,637 current smokers. We also examined trends for individual NDSS sub-scales and whether trends were moderated by tobacco consumption and socio-demographic factors. Results: Consumption levels and dependence severity both declined over the study period. This decline was driven by priority (e.g., avoiding smoke-free locations) and tolerance dimensions of dependence, while drive (e.g., craving and smoking to relieve negative affect) and continuity (e.g., stability) of smoking did not change. Declines for tolerance were greatest among those without serious psychological distress and among middle-aged smokers. Drive and continuity increased among women and low income smokers. Conclusions: We did not find evidence of hardening at the population level for smokers in the U.S., 2002-2012. However, there is evidence of hardening when considering drive and continuity-related nicotine dependence among women and low-income smokers, suggesting these sub-groups are experiencing greater severity of craving, smoking to relieve negative affect, and regularity of smoking despite reduced consumption. (C) 2014 Elsevier Ireland Ltd. All rights reserved.