Hardening or softening? An observational study of changes to the prevalence of hardening indicators in Victoria, Australia, 2001–2016

Background The hardening hypothesis predicts that as smoking prevalence declines, remaining smokers will be more heavily addicted to nicotine and/or less interested in quitting. We tested this hypothesis in a population exposed to a comprehensive tobacco control programme over a 16-year period. Methods Annual cross-sectional surveys randomly sampled adults (aged 26+) in the state of Victoria, Australia, between 2001 and 2016. Until 2010, participants were recruited through random digit dialling to landline telephones; from 2011, sampling frames also included mobile phones. Logistic regressions assessed changes over time in the prevalence of smoking and each hardening indicator; additional models examined interactions by sex, age, education and socioeconomic status. Results Smoking prevalence declined significantly between 2001 and 2016 (20.1%–13.0%), as did the prevalence of seven hardening indicators: daily smoking, heavy consumption, no quit attempt in the past 5 years or past 12 months, no intention to quit in the next 6 months or next 30 days, and happiness to keep smoking. In addition, the proportion of smokers defined as ‘hardcore’ decreased from 17.2% to 9.1%. On the whole, hardening indicators decreased to a similar extent among demographic subgroups. Conclusions These results are inconsistent with the hardening hypothesis. Rather, they suggest that a comprehensive tobacco control programme that combines provision of cessation support to individual smokers with implementation of population-level interventions to drive all smokers towards quitting, can successfully reduce both smoking prevalence and levels of dependence and desire to keep smoking among the remaining population of smokers.