The Heaviness of Smoking Index as a predictor of smoking cessation in Canada
Introduction
A variety of researchers and clinicians have speculated that the current smoking population in Canada and other developed countries may be becoming more and more resistant to quitting smoking (Fagerstrom et al., 1996, Jarvis et al., 2003). It is believed that smokers who are less addicted to nicotine quit smoking at greater rates, leaving a larger proportion of heavily addicted (so-called “hard core”) smokers in the population (Breslau et al., 2001, Fagerstrom et al., 1996, Hughes, 2001, Irvin and Brandon, 2000, Niaura et al., 1994, Warner and Burns, 2003). If this hypothesis is true, it would have significant implications for the development of a future population strategy for smoking cessation. Therefore, understanding potential changes in the level of nicotine dependence in the population, and its relation to quitting, is crucial.
Nicotine dependence is a distinct concept from the act of cigarette smoking and refers to the propensity of an individual's need for nicotine. Some conceptions of dependence suggest that it may reflect a physiological-based requirement implicit in an individual (Kemmeren, van Poppel, Verhoef & Jarvis, 1994). Studies within families have demonstrated a genetic influence on nicotine dependence (Henningfield, 1990, Kendler et al., 1999, Niu et al., 2000).
The most common clinical measure of nicotine dependence is the Fagerstrom Tolerance Questionnaire (Fagerstrom, 1978, Fagerstrom and Schneider, 1989, Heatherton et al., 1991, Heatherton et al., 1989). While it is a relatively brief tool for clinical assessment, its length is still a problem for population-based surveys. Therefore, the Heaviness of Smoking Index (HSI) was developed in 1989 as a test to measure the same construct by using two questions from the Tolerance Questionnaire and the Fagerstrom Test for Nicotine Dependence: time to first smoking in the morning and number of cigarettes per day (Kozlowski, Porter, Orleans, Pope, & Heatherton, 1994). These questions were shown to have accounted for most of the predictive value of the Fagerstrom questionnaire and have been validated as providing similar results (Etter et al., 1999, Heatherton et al., 1989, Kozlowski et al., 1994). The Fagerstrom tests are purported to proxy the physical addiction to nicotine and not to correspond to compulsive or habitual smoking (Dijkstra and Tromp, 2002, Fagerstrom, 1978).
While these measures of nicotine dependence have been shown to be significantly associated with smoking cessation in many studies (de Leon et al., 2003, Fagerstrom and Schneider, 1989, Heatherton et al., 1991, Heatherton et al., 1989, Kozlowski et al., 1994, Payne et al., 1994), a number of studies have found either no relationship or one that is less predictive of quitting than number of cigarettes per day (Dijkstra and Tromp, 2002, Frikart et al., 2003, McDonald, 2003, Salive et al., 1992, Wetter et al., 1994).
All else being equal, it can be assumed that the connection between increasing levels of dependence and smoking cessation would be clear; however, dependence is only one factor in making, and succeeding, at a quit attempt. While the physical dependence model of nicotine dependence is widely accepted, many questions remain as to the nature of its definition, and importance with respect to other models; nevertheless, a common trait between competing theoretical models is that dependence entails a difficulty in achieving abstinence (Kenford et al., 2002). However, it is not clear how well measures of dependence adequately conceptualize dependence. Attempts to link measures of physical dependence with mechanisms that could explain the ability or the inability to quit smoking have met with limited success (Kenford et al., 2002). The purpose of this paper is to examine whether there is a relationship between self-report nicotine dependency and the likelihood of subsequent smoking cessation in the general population.
Section snippets
Design
This study used the longitudinal panel data set from the population-based National Population Health Survey (NPHS), cycle 2 (1996–1997), cycle 3 (1998–1999), and cycle 4 (2000–2001). The original sample, cycle 1 (1994–1995), was not used as it did not measure both items needed to calculate HSI.
Respondents from 19,600 households were recruited in 1994–1995 by random digit dialling, stratified to ensure adequate provincial coverage and sampled to reflect the general Canadian population (Tambay &
Results
Of the survey participants included in this study, 47% were older than 40 years of age, 53% were males, 19% reported below middle income adequacy, 54% had formal education beyond a high school degree (e.g. at least some technical college or university), and 46% reported an intention to quit within the next 6 months (Table 1). Almost a majority (45%) of daily smokers reported smoking between 11 and 20 cigarettes per day, while the most commonly reported (36%) time to first cigarette was between
Discussion
This study found that HSI is associated with reported changes in smoking status in Canada. Smokers who had low HSI scores were more likely to have reported quitting at follow-up. However, unexpectedly, the data did not indicate a constant negative linear relationship between increasing HSI scores and a decreasing probability of cessation at follow-up. Smokers with high HSI scores were more likely to report not smoking at both cycle 3 and cycle 4 than smokers with medium scores.
While unexpected,
Acknowledgements
Support for Michael O. Chaiton was provided by the Canadian Institutes of Health Research Strategic Training Program for Tobacco Research. Funding for Paul W. McDonald came, in part, from the Heart and Stroke Foundation of Ontario, Grant Number HBR 4858.
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