Review of evidence regarding attributes and behaviours of smokers as smoking prevalence falls, including evidence relevant to the ‘hardening hypothesis’

Abstract

AbstractTo review evidence relevant to Australia and similar high-income countries regarding continuing smokers’ motivation, dependence and quitting behaviour as smoking prevalence declines, to assess whether population “hardening” (decreasing propensity to quit) or “softening” (the converse) is occurring. MEDLINE, PsychINFO, Scopus, Web of Science and Cochrane Library were searched to July 2019, using terms related to smoking and hardening, for reviews and large, population-based repeat cross-sectional studies. There were additional searches of reference lists and citations of key research articles. Two reviewers screened half the titles and abstracts each, and two reviewers screened all full texts independently using tested criteria. Four reviewers independently and systematically extracted data from eligible publications, with one reviewer per study, checked by another reviewer. Of 265 titles identified, three reviews and ten repeat cross-sectional studies (not included in the reviews) were included. All three reviews concluded that hardening has not occurred among the general smoking population over time. Of the ten repeated cross-sectional studies, five examined motivation, nine examined dependence, five examined hardcore smoking, and two examined quit outcomes over time. All found a lack of hardening and most found softening within the smoking population, consistent across hardening indicators, definitions, countries (and tobacco control environments) and time periods examined. Declining smoking prevalence has been accompanied by softening within the population of smokers, characterised by increasing motivation to quit and reduced dependency. Based on the weight of the available evidence from high-income countries, the “hardening hypothesis” should be rejected.