Professor Richard Edwards
The hardening hypothesis suggests that as smoking prevalence declines, the remaining smokers will be the more addicted ones who are less likely to quit. But does the NZ evidence support this? This blog considers these issues and explores the potential implications for achieving NZ’s Smokefree 2025 goal.
The ‘hardening hypothesis’ emerged in the 1980s and proposed that as smoking prevalence declines the remaining smokers will increasingly be ‘hard-core’ or ‘hardened’, with higher nicotine dependence and less willingness to quit. The logic is appealing, as it seems common-sense that lighter and more motivated smokers will be over-represented and hard-core smokers under-represented among those quitting. If true it would support the views of the people who say to me with wearying regularity when I mention New Zealand’s Smokefree 2025 goal – “lovely idea, but completely impossible, it’ll never happen,” or words to that effect.
There is one problem with this hypothesis. Almost all the empirical evidence suggests it is not true.
There are several ways in which hardening could manifest and hence the hypothesis can be tested. The population of smokers could become: (i) more highly addicted (eg, heavier smokers, more dependent); (ii) less motivated to quit (eg, less intention to quit, fewer quit attempts, lower self-efficacy about ability to quit); and (iii) increasingly disadvantaged and marginalised (eg, more poor smokers, more smokers with mental health conditions). The net effect should be a reduced rate of quitting among the smoking population over time. However, studies from a variety of countries that have looked at these different aspects either singly or in combination in repeated surveys have generally found no evidence of hardening (1-11).
The most recent international evidence comes from a Dutch study which found that in repeated population-based surveys the proportion of ‘hard-core’ smokers (older than 25 years, smoked every day, smoked 15+ cigarettes per day, had not attempted to quit in the past year, and had no intention to quit within 6 months) fell from 41% in 2001 to 32% in 2012 (12). Another recent study investigated whether, as predicted by the hardening hypothesis, lower smoking prevalence at the population level was associated with increasing mean number of cigarettes smoked per day and a declining proportion making quit attempts among smokers in US States (1992-2011) and 31 European countries (2006-2012). The authors found mostly the opposite, and argued this was consistent with ‘softening’ of the smoking population occurring with reducing smoking prevalence (13).
What about New Zealand research?
A recent paper (Edwards et al in the journal Tobacco Control (14)) drawing on evidence from the Health Promotion Agency’s Health and Lifestyle surveys from 2008-2014, mirrored the findings of the studies described above. During a period of reducing smoking prevalence, there were no statistically significant changes in indicators of possible hardening including the proportion of smokers who were: unmotivated to quit, unable to quit despite repeated attempts, or receiving state benefits or on a low income. Quit rates did not change significantly over the study period. For 2014 vs 2008 the odds ratio for recent (within last 1-12 months) quitting was 1.14 (95% CI: 0.53-2.46) and for sustained (within previous 13-24 months) quitting was 1.88 (95% CI: 0.78-4.54). The findings were similar for Māori smokers. The survey did not include information on levels of addiction, but in the NZ Health Survey, there were statistically significant reductions in the mean numbers of cigarettes smoked per day by daily smokers from 11.5 in 2006/7 (11.6 among Māori) to 10.6 (10.3 among Māori) in 2014/15 (15).
So what might all this mean for NZ’s Smokefree 2025 goal?
There are two key implications. The first concerns how we should achieve Smokefree 2025. If hardening was happening, this would suggest that we need to rethink what interventions at individual-level (eg, configuration of smoking cessation support services) and population-level (eg, mix of smokefree policy and regulatory measures) are implemented. However, the lack of evidence for hardening does not support the need for such a rethink, though it may well be needed for other reasons – such as evidence that ongoing prevalence reductions are too slow, particularly among Māori and that some measures like mass media campaigns and reducing supply of tobacco products are inadequately implemented (16-18).
A second implication is that although there are reasons to be doubtful about the achievability of Smokefree 2025 by this particular year – for example, due to lack of a Government action plan and failure to progress key interventions (19), – the evidence favouring softening rather than hardening, suggests there is room for optimism about ongoing progress. Indeed, in some ways it is not surprising that the smoker population is ‘softening’ ie, becoming less addicted, more motivated to quit and more likely to quit. Measures used in NZ such as regular above inflation tobacco tax increases, expansion of smokefree areas, pictorial health warnings on packs coupled with denormalisation from the reducing prevalence of smokers, all seem likely to prompt such changes in the smoking population. Intensification of these measures and introduction of additional measures are likely to enhance this apparent softening.
So a plausible conclusion from all this is as follows. If the necessary interventions were put in place – and the key recommendations of the Smokefree Working Group would be a great start (20), – then there is every reason to believe that NZ’s Smokefree 2025 goal can and will be achieved.
1. Al-Delaimy WK, Pierce JP, Messer K, White MM, Trinidad DR, Gilpin EA. The California Tobacco Control Program’s effect on adult smokers: (2) Daily cigarette consumption levels. Tob Control. 2007;16:91-5.
2. Burns DM, Major JM, Anderson CM, Vaughan JW. Changes in cross-sectional measures of cessation, numbers of cigarettes smoked per day, and time to first cigarette-California and national data. Those Who Continue To Smoke: Is Achieving Abstinence Harder and Do We Need to Change Our Interventions Smoking and Tobacco Control Monograph 15. Bethesda: U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, National Cancer Institute, 2003; pp101-25.
3. Celebucki C, Brawarsky P. Hardening of the target: Evidence from Massachusetts. Those Who Continue To Smoke: Is Achieving Abstinence Harder and Do We Need to Change Our Interventions Smoking and Tobacco Control Monograph 15. Bethesda: U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, National Cancer Institute, 2003; pp127-45.
4. Clare P, Bradford D, Courtney RJ, Martire K, Mattick RP. The relationship between socioeconomic status and ‘hardcore’ smoking over time – greater accumulation of hardened smokers in low-SES than high-SES smokers. Tob Control. 2014;23(e2):e133-8.
5. Gartner C, Scollo M, Marquart L, Mathews R, Hall W. Analysis of national data shows mixed evidence of hardening among Australian smokers. Aust N Z J Public Health. 2012;36:408-14.
6. Jarvis MJ, Giovino GA, O’Connor RJ, Kozlowski LT, Bernert JT. Variation in nicotine intake in US cigarette smokers over the past 25 years: evidence from NHANES surveys. Nicotine & Tobacco Research. 2014;16:1620-8.
7. Lund M, Lund KE, Kvaavik E. Hardcore smokers in Norway 1996-2009. Nicotine Tob Res. 2011;13:1132-9.
8. Mathews R, Hall WD, Gartner CE. Is there evidence of ‘hardening’among Australian smokers between 1997 and 2007? Analyses of the Australian National Surveys of Mental Health and Well-Being. Aust N Z J Psychiatry. 2010;44:1132-6.
9. Messer K, Pierce JP, Zhu SH, et al. The California Tobacco Control Program’s effect on adult smokers: (1) Smoking cessation. Tob Control. 2007;16:85-90.
10. O’Connor RJ, Giovino GA, Kozlowski LT, et al. Changes in nicotine intake and cigarette use over time in two nationally representative cross-sectional samples of smokers. Am J Epidemiol. 2006;164:750-9.
11. Pierce JP, Messer K, White MM, Cowling DW, Thomas DP. Prevalence of heavy smoking in California and the United States, 1965-2007. JAMA. 2011;305:1106-12.
12. Bommele J, Nagelhout GE, Kleinjan M, Schoenmakers TM, Willemsen MC, van de Mheen D. Prevalence of hardcore smoking in the Netherlands between 2001 and 2012: a test of the hardening hypothesis. BMC Public Health. 2016;16:754.
13. Kulik MC, Glantz SA. The smoking population in the USA and EU is softening not hardening. Tob Control. 2016;25:470-5.
14. Edwards R, Tu D, Newcombe R, Holland K, Walton D. Achieving the tobacco endgame: evidence on the hardening hypothesis from repeated cross-sectional studies in New Zealand 2008–2014. Tob Control. 2016:tobaccocontrol-2015-052860.
15. Ministry of Health. Annual Update of Key Results 2014/15: New Zealand Health Survey. Adult data tables: health status, health behaviours and risk factors (accessed August 13 2016). Annual Update of Key Results 2014/15: New Zealand Health Survey. Wellington: Ministry of Health, 2016.
16. Cobiac LJ, Ikeda T, Nghiem N, Blakely T, Wilson N. Modelling the implications of regular increases in tobacco taxation in the tobacco endgame. Tob Control. 2015;24(e2):e154-60.
17. van der Deen FS, Ikeda T, Cobiac L, Wilson N, Blakely T. Projecting future smoking prevalence to 2025 and beyond in New Zealand using smoking prevalence data from the 2013 Census. N Z Med J. 2013;127:71-9.
18. Ball J, Stanley J, Wilson N, Blakely T, Edwards R. Smoking prevalence in New Zealand from 1996–2015: a critical review of national data sources to inform progress toward the smokefree 2025 goal. N Z Med J. 2016;129:1439.
19. Ball J, Edwards R, Waa A, et al. Is the NZ Government responding adequately to the Māori Affairs Select Committee’s 2010 recommendations on tobacco control? A brief review. N Z Med J 2016;129(1428):93-7.
20. National Smokefree Working Group. Smokefree Aotearoa 2025: Action Plan 2015-2018. Wellington: National Smokefree Working Group, 2015.