Nicotine & Tobacco Research, Volume 16, Number 12 (December 2014) 1537–1538
Commentary
Rigorous Methodoloy Is Needed to Analyze and Interpret Observational Data on the Use and Effectiveness of Smoking Cessation Aids Daniel Kotz PhD1,2 1Department of Family Medicine, CAPHRI School for Public Health and Primary Care, Maastricht University Medical Centre, Maastricht, the Netherlands; 2Cancer Research UK Health Behavior Research Centre, University College London, London, UK
Corresponding Author: Daniel Kotz, PhD, Department of Family Medicine, CAPHRI School for Public Health and Primary Care, Maastricht University Medical Centre, PO Box 616, 6200 MD Maastricht, the Netherlands. Telephone: 31-43-3882893; Fax: 31-43-3619344; E-mail: [email protected]
In the current issue, Clare et al.1 present data from 23,402 respondents (of which 18% were recent ex-smokers) to four waves of an Australian household survey to address two research questions: (a) whether use of smoking cessation aids differed by indicators of socioeconomic status; (b) whether smoking status differed by use of smoking cessation aids. Advantages of a study using such household data include large statistical power and high level of external validity. However, the internal validity of a study that relies on relatively crude, observational data can be limited. The biggest threat to the internal validity of an observational study—especially a cross-sectional study—on the use and effectiveness of smoking cessation aids is potential bias due to confounding. The most important confounding factor in this respect is tobacco dependence. A simple analysis of the association between socioeconomic status and use of smoking cessation aids is confounded because socioeconomic status is associated with dependence,2 and smokers who are more dependent are more likely to use pharmacotherapy to treat their dependence.3–6 Similarly, an analysis of the association between use of smoking cessation aids and abstinence is confounded because, again, smokers who are more dependent are more likely to use pharmacotherapy to treat their dependence, and smokers who are more dependent have a lower chance of achieving abstinence.7 An analysis that does not adequately adjust for differences in dependence would lead to an underestimation of the effect of pharmacotherapy. Clare et al.1 adjusted their analysis of the association between smoking cessation aids and abstinence from smoking only for several demographic and socioeconomic variables (Table S2). Thus, their results on the relative effectiveness of the various smoking cessation aids are difficult to interpret. Adjusting the analysis of cross-sectional data for the confounder tobacco dependence is challenging because, dependence measures that include an estimate for cigarettes smoked per day are not valid in respondents who are recent ex-smokers like in the study by Clare et al.1 A better method, recently introduced, uses ratings of urges to smoke for this purpose.8
Second, detailed information is needed on the exact type of smoking cessation aid used by the respondents to a survey. Nicotine replacement therapy (NRT), for example, is available in many countries both on prescription as well as overthe-counter medication, but its effectiveness may be higher if provided with brief advice by the prescribing healthcare professional.8 Thus, the level of behavioral support provided together with the medication can make a difference. Clare et al.1 categorized pharmacotherapies into “patches, gum, or inhaler,” “prescription medication, for example, Zyban,” and “other smoking medication.” Here, it is unclear whether the category “patches, gum, or inhaler” referred to over-the-counter NRT and/or to prescription NRT, and whether the category “prescription medication” also included NRT. It is also not clear with which level of behavioral support the medication was provided. A study in the U.S. population (not discussed by Clare et al.) showed that the use of any behavioral treatment and any pharmacological treatment increased with increasing household income, but household income was not associated with use of type of NRT (NRT on prescription versus overthe-counter).9 A more recent study in the English population showed that prescription medication (NRT, bupropion, or varenicline) combined with brief advice by the prescribing healthcare provider was associated with an increased chance of abstinence from smoking compared with unaided quitting, whereas NRT bought over-the-counter was not.8 Furthermore, prescription medication combined with specialist behavioral support (i.e., one-to-one or group behavioral support delivered by a National Health Service Stop Smoking Service) was more effective than prescription medication combined with brief advice.8 Third, it is important to have information on the use of aids during the most recent quit attempt to avoid misclassification. Clare et al.1 included respondents who had smoked in the 12 months prior to the survey and asked if they had used any of a number of smoking cessation aids (e.g., “used patches” or “called a quit line”), but without specifically relating their use to the most recent quit attempt. Whereas indicators of
doi:10.1093/ntr/ntu142 Advance Access publication October 15, 2014 © The Author 2014. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved. For permissions, please e-mail: [email protected].
1537
Downloaded from http://ntr.oxfordjournals.org/ at University of California, Davis on January 30, 2015
Received June 30, 2014; accepted July 10, 2014
Rigorous methodoloy is needed to analyze and interpret observational data
Funding None declared.
Declaration of Interests None declared.
1538
References Clare P, Slade T, Courtney R, Martire K, Mattick R. The use of smoking cessation and quit support services by socioeconomic status over 10 years of the National Drug Strategy Household Survey. Nicotine Tob Res. Kotz D, West R. Explaining the social gradient in smoking cessation: it’s not in the trying, but in the succeeding. Tob Control. 2009;18:43–46. Borland R, Partos TR, Cummings KM. Systematic biases in cross-sectional community studies may underestimate the effectiveness of stop-smoking medications. Nicotine Tob Res. 2012;14:1483–1487. Hughes JR, Peters EN, Naud S. Effectiveness of over-thecounter nicotine replacement therapy: a qualitative review of nonrandomized trials. Nicotine Tob Res. 2011;13:512–522. Shiffman S, Di Marino ME, Sweeney CT. Characteristics of selectors of nicotine replacement therapy. Tob Control. 2005;14:346–355. West R, Zhou X. Is nicotine replacement therapy for smoking cessation effective in the “real world”? Findings from a prospective multinational cohort study. Thorax. 2007;62:998–1002. Vangeli E, Stapleton J, Smit ES, Borland R, West R. Predictors of attempts to stop smoking and their success in adult general population samples: a systematic review. Addiction. 2011;106:2110–2121. Kotz D, Brown J, West R. ‘Real-world’ effectiveness of smoking cessation treatments: a population study. Addiction. 2014;109:491–499. Shiffman S, Brockwell SE, Pillitteri JL, Gitchell JG. Individual differences in adoption of treatment for smoking cessation: demographic and smoking history characteristics. Drug Alcohol Depend. 2008;93:121–131.
Downloaded from http://ntr.oxfordjournals.org/ at University of California, Davis on January 30, 2015
socioeconomic status can be regarded as stable over a period of 12 months, this is not the case for the use of aids to cessation because smokers can make multiple attempts to quit during the course of a year and may use a different aid or no aid at all during each attempt. Misclassification may then occur, for example, in recent ex-smokers who tried to quit by calling a quit line during their most recent quit attempt and are still abstinent at the time of the survey but who used patches during one of their previous attempts in the same year and relapsed; the association between socioeconomic status and use of patches as well as the association between use of patches and abstinence would be biased in this case. In conclusion, population surveys can be an important source of data to assess the use and effectiveness of smoking cessation treatments in the “real world” and can supplement evidence from randomized controlled trials. However, analyses of observational data can be biased and their results misleading. Therefore, a rigorous methodology for such analyses is needed, including a clear definition of types of aids used during the most recent quit attempt and statistical adjustment for potential confounders, most importantly tobacco dependence.
Commentary
Rigorous Methodoloy Is Needed to Analyze and Interpret Observational Data on the Use and Effectiveness of Smoking Cessation Aids Daniel Kotz PhD1,2 1Department of Family Medicine, CAPHRI School for Public Health and Primary Care, Maastricht University Medical Centre, Maastricht, the Netherlands; 2Cancer Research UK Health Behavior Research Centre, University College London, London, UK
Corresponding Author: Daniel Kotz, PhD, Department of Family Medicine, CAPHRI School for Public Health and Primary Care, Maastricht University Medical Centre, PO Box 616, 6200 MD Maastricht, the Netherlands. Telephone: 31-43-3882893; Fax: 31-43-3619344; E-mail: [email protected]
In the current issue, Clare et al.1 present data from 23,402 respondents (of which 18% were recent ex-smokers) to four waves of an Australian household survey to address two research questions: (a) whether use of smoking cessation aids differed by indicators of socioeconomic status; (b) whether smoking status differed by use of smoking cessation aids. Advantages of a study using such household data include large statistical power and high level of external validity. However, the internal validity of a study that relies on relatively crude, observational data can be limited. The biggest threat to the internal validity of an observational study—especially a cross-sectional study—on the use and effectiveness of smoking cessation aids is potential bias due to confounding. The most important confounding factor in this respect is tobacco dependence. A simple analysis of the association between socioeconomic status and use of smoking cessation aids is confounded because socioeconomic status is associated with dependence,2 and smokers who are more dependent are more likely to use pharmacotherapy to treat their dependence.3–6 Similarly, an analysis of the association between use of smoking cessation aids and abstinence is confounded because, again, smokers who are more dependent are more likely to use pharmacotherapy to treat their dependence, and smokers who are more dependent have a lower chance of achieving abstinence.7 An analysis that does not adequately adjust for differences in dependence would lead to an underestimation of the effect of pharmacotherapy. Clare et al.1 adjusted their analysis of the association between smoking cessation aids and abstinence from smoking only for several demographic and socioeconomic variables (Table S2). Thus, their results on the relative effectiveness of the various smoking cessation aids are difficult to interpret. Adjusting the analysis of cross-sectional data for the confounder tobacco dependence is challenging because, dependence measures that include an estimate for cigarettes smoked per day are not valid in respondents who are recent ex-smokers like in the study by Clare et al.1 A better method, recently introduced, uses ratings of urges to smoke for this purpose.8
Second, detailed information is needed on the exact type of smoking cessation aid used by the respondents to a survey. Nicotine replacement therapy (NRT), for example, is available in many countries both on prescription as well as overthe-counter medication, but its effectiveness may be higher if provided with brief advice by the prescribing healthcare professional.8 Thus, the level of behavioral support provided together with the medication can make a difference. Clare et al.1 categorized pharmacotherapies into “patches, gum, or inhaler,” “prescription medication, for example, Zyban,” and “other smoking medication.” Here, it is unclear whether the category “patches, gum, or inhaler” referred to over-the-counter NRT and/or to prescription NRT, and whether the category “prescription medication” also included NRT. It is also not clear with which level of behavioral support the medication was provided. A study in the U.S. population (not discussed by Clare et al.) showed that the use of any behavioral treatment and any pharmacological treatment increased with increasing household income, but household income was not associated with use of type of NRT (NRT on prescription versus overthe-counter).9 A more recent study in the English population showed that prescription medication (NRT, bupropion, or varenicline) combined with brief advice by the prescribing healthcare provider was associated with an increased chance of abstinence from smoking compared with unaided quitting, whereas NRT bought over-the-counter was not.8 Furthermore, prescription medication combined with specialist behavioral support (i.e., one-to-one or group behavioral support delivered by a National Health Service Stop Smoking Service) was more effective than prescription medication combined with brief advice.8 Third, it is important to have information on the use of aids during the most recent quit attempt to avoid misclassification. Clare et al.1 included respondents who had smoked in the 12 months prior to the survey and asked if they had used any of a number of smoking cessation aids (e.g., “used patches” or “called a quit line”), but without specifically relating their use to the most recent quit attempt. Whereas indicators of
doi:10.1093/ntr/ntu142 Advance Access publication October 15, 2014 © The Author 2014. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved. For permissions, please e-mail: [email protected].
1537
Downloaded from http://ntr.oxfordjournals.org/ at University of California, Davis on January 30, 2015
Received June 30, 2014; accepted July 10, 2014
Rigorous methodoloy is needed to analyze and interpret observational data
Funding None declared.
Declaration of Interests None declared.
1538
References Clare P, Slade T, Courtney R, Martire K, Mattick R. The use of smoking cessation and quit support services by socioeconomic status over 10 years of the National Drug Strategy Household Survey. Nicotine Tob Res. Kotz D, West R. Explaining the social gradient in smoking cessation: it’s not in the trying, but in the succeeding. Tob Control. 2009;18:43–46. Borland R, Partos TR, Cummings KM. Systematic biases in cross-sectional community studies may underestimate the effectiveness of stop-smoking medications. Nicotine Tob Res. 2012;14:1483–1487. Hughes JR, Peters EN, Naud S. Effectiveness of over-thecounter nicotine replacement therapy: a qualitative review of nonrandomized trials. Nicotine Tob Res. 2011;13:512–522. Shiffman S, Di Marino ME, Sweeney CT. Characteristics of selectors of nicotine replacement therapy. Tob Control. 2005;14:346–355. West R, Zhou X. Is nicotine replacement therapy for smoking cessation effective in the “real world”? Findings from a prospective multinational cohort study. Thorax. 2007;62:998–1002. Vangeli E, Stapleton J, Smit ES, Borland R, West R. Predictors of attempts to stop smoking and their success in adult general population samples: a systematic review. Addiction. 2011;106:2110–2121. Kotz D, Brown J, West R. ‘Real-world’ effectiveness of smoking cessation treatments: a population study. Addiction. 2014;109:491–499. Shiffman S, Brockwell SE, Pillitteri JL, Gitchell JG. Individual differences in adoption of treatment for smoking cessation: demographic and smoking history characteristics. Drug Alcohol Depend. 2008;93:121–131.
Downloaded from http://ntr.oxfordjournals.org/ at University of California, Davis on January 30, 2015
socioeconomic status can be regarded as stable over a period of 12 months, this is not the case for the use of aids to cessation because smokers can make multiple attempts to quit during the course of a year and may use a different aid or no aid at all during each attempt. Misclassification may then occur, for example, in recent ex-smokers who tried to quit by calling a quit line during their most recent quit attempt and are still abstinent at the time of the survey but who used patches during one of their previous attempts in the same year and relapsed; the association between socioeconomic status and use of patches as well as the association between use of patches and abstinence would be biased in this case. In conclusion, population surveys can be an important source of data to assess the use and effectiveness of smoking cessation treatments in the “real world” and can supplement evidence from randomized controlled trials. However, analyses of observational data can be biased and their results misleading. Therefore, a rigorous methodology for such analyses is needed, including a clear definition of types of aids used during the most recent quit attempt and statistical adjustment for potential confounders, most importantly tobacco dependence.
