Tobacco
Quitting activity and tobacco brand switching
References
adjusted for in the analysis, possibly because changes in the price of survey respondents’ usual brand of cigarette were not recorded in ITC-4. Cowie and colleagues attempted to minimise the effects of selection bias and confounding by using GEE to adjust for three potential confounding factors (age, sex and income). Ideally, these models would have adjusted for additional factors such as cigarettes smoked per day and nicotine dependence. Using appropriate statistical techniques to adjust for a sufficiently large number of confounding factors in observational data can dramatically alter the results. This was illustrated in a trial that showed that use of electronic cigarettes was significantly associated with lower abstinence; however, the association was no longer significant when entropy balancing was employed to adjust for concurrent use of other cessation aids.4 Cowie and colleagues have attempted the very difficult task of using an observational study to test for causality. Their analyses appear to show that smokers who aim to quit in the near future are more likely to switch brands than those who are less interested in quitting in the short-term. However, smokers who plan to quit in the near future tend not to switch brands prior to quitting but rather do so only after failing to quit. Therefore, switching brands is a sign that smokers are interested in quitting, but need more help to quit. Smokers need to be informed that switching brands will not necessarily help them to quit, and that if they are having difficulty quitting it may be more effective for them to use nicotine replacement therapy than to change their brand of cigarettes.
2015 vol. 39 no. 2
1. Cowie A, Swift E, Partos T, Borland R. Quitting activity and tobacco brand Switching: findings from the ITC-4 Country Survey. Aust N Z J Public Health. 2015; 39(2):9-13 2. Hill AB. The Environment and Disease: Association or Causation? Proceedings of the Royal Society of Medicine 1965;58(5):295-300. 3. Thompson ME, Fong GT, Hammond D, Boudreau C, Driezen P, Hyland A, Borland R, Cummings KM, Hastings GB, Siahpush M, Mackintosh AM, Laux FL. Methods of the International Tobacco Control (ITC) Four Country Survey. Tobacco Control 2006;15 Suppl 3:iii12-8. 4. Pearson JL, Stanton CA, Cha S, Niaura RS, Luta G, Graham AL. E-cigarettes and smoking cessation: Insights and cautions from a secondary analysis of data from a study of online treatment-seeking smokers. Nicotine & Tobacco Research 2014.
Correspondence to: Dr Brent Caldwell, Department of Medicine, University of Otago, PO Box 7343, Wellington 6021, New Zealand; e-mail: [email protected]
doi: 10.1111/1753-6405.12383
Unpicking causal possibilities: Authors’ response to Caldwell Genevieve A. Cowie,1 Elena Swift,2 Timea Partos,2 Ron Borland2 1. Department of Epidemiology & Preventive Medicine, School of Public Health & Preventive Medicine, Monash University, Victoria 2. Cancer Council Victoria
We agree with Caldwell, both that RCTs are the only fail-safe method for showing causal associations and that such an approach was not an option here. However, we add one other important reason. An RCT can only test possible causal factors that are under the researcher’s control. Brand switching is a personal choice. Thus, even an RCT of forced
brand switching would not provide direct evidence of the causal impact of a chosen switch: the two are very different. This is a problem that effectively precludes adequately controlled RCTs for many behavioural interventions: we can offer them to people, but can’t expect pre-commitment without first describing the different requirements of the various experimental conditions, thus creating different expectancies. In the more focussed comments, Caldwell argues that relative price might be a confounder for the asymmetrical relationships we found. However, price is an unlikely confounder; if switching to a cheaper brand was an alternative to quitting, we might expect switching to be associated with less subsequent quit interest. However we found the reverse asymmetry - the interest to switching association was stronger. Controlling for dependence made no difference to the findings. We believe our modest claims as to which causal direction was most likely are reasonable, as apparently does Caldwell, given his take out message is essentially the same as ours. Looking for asymmetrical relationships is a useful way of testing potential causal models where RCT evidence is not available, or in this case not achievable. Correspondence to: Dr Ron Borland, Cancer Council Victoria, 615 St Kilda Rd, Melbourne, VIC 3004; e-mail: [email protected]
Australian and New Zealand Journal of Public Health © 2015 Public Health Association of Australia
115
Quitting activity and tobacco brand switching
References
adjusted for in the analysis, possibly because changes in the price of survey respondents’ usual brand of cigarette were not recorded in ITC-4. Cowie and colleagues attempted to minimise the effects of selection bias and confounding by using GEE to adjust for three potential confounding factors (age, sex and income). Ideally, these models would have adjusted for additional factors such as cigarettes smoked per day and nicotine dependence. Using appropriate statistical techniques to adjust for a sufficiently large number of confounding factors in observational data can dramatically alter the results. This was illustrated in a trial that showed that use of electronic cigarettes was significantly associated with lower abstinence; however, the association was no longer significant when entropy balancing was employed to adjust for concurrent use of other cessation aids.4 Cowie and colleagues have attempted the very difficult task of using an observational study to test for causality. Their analyses appear to show that smokers who aim to quit in the near future are more likely to switch brands than those who are less interested in quitting in the short-term. However, smokers who plan to quit in the near future tend not to switch brands prior to quitting but rather do so only after failing to quit. Therefore, switching brands is a sign that smokers are interested in quitting, but need more help to quit. Smokers need to be informed that switching brands will not necessarily help them to quit, and that if they are having difficulty quitting it may be more effective for them to use nicotine replacement therapy than to change their brand of cigarettes.
2015 vol. 39 no. 2
1. Cowie A, Swift E, Partos T, Borland R. Quitting activity and tobacco brand Switching: findings from the ITC-4 Country Survey. Aust N Z J Public Health. 2015; 39(2):9-13 2. Hill AB. The Environment and Disease: Association or Causation? Proceedings of the Royal Society of Medicine 1965;58(5):295-300. 3. Thompson ME, Fong GT, Hammond D, Boudreau C, Driezen P, Hyland A, Borland R, Cummings KM, Hastings GB, Siahpush M, Mackintosh AM, Laux FL. Methods of the International Tobacco Control (ITC) Four Country Survey. Tobacco Control 2006;15 Suppl 3:iii12-8. 4. Pearson JL, Stanton CA, Cha S, Niaura RS, Luta G, Graham AL. E-cigarettes and smoking cessation: Insights and cautions from a secondary analysis of data from a study of online treatment-seeking smokers. Nicotine & Tobacco Research 2014.
Correspondence to: Dr Brent Caldwell, Department of Medicine, University of Otago, PO Box 7343, Wellington 6021, New Zealand; e-mail: [email protected]
doi: 10.1111/1753-6405.12383
Unpicking causal possibilities: Authors’ response to Caldwell Genevieve A. Cowie,1 Elena Swift,2 Timea Partos,2 Ron Borland2 1. Department of Epidemiology & Preventive Medicine, School of Public Health & Preventive Medicine, Monash University, Victoria 2. Cancer Council Victoria
We agree with Caldwell, both that RCTs are the only fail-safe method for showing causal associations and that such an approach was not an option here. However, we add one other important reason. An RCT can only test possible causal factors that are under the researcher’s control. Brand switching is a personal choice. Thus, even an RCT of forced
brand switching would not provide direct evidence of the causal impact of a chosen switch: the two are very different. This is a problem that effectively precludes adequately controlled RCTs for many behavioural interventions: we can offer them to people, but can’t expect pre-commitment without first describing the different requirements of the various experimental conditions, thus creating different expectancies. In the more focussed comments, Caldwell argues that relative price might be a confounder for the asymmetrical relationships we found. However, price is an unlikely confounder; if switching to a cheaper brand was an alternative to quitting, we might expect switching to be associated with less subsequent quit interest. However we found the reverse asymmetry - the interest to switching association was stronger. Controlling for dependence made no difference to the findings. We believe our modest claims as to which causal direction was most likely are reasonable, as apparently does Caldwell, given his take out message is essentially the same as ours. Looking for asymmetrical relationships is a useful way of testing potential causal models where RCT evidence is not available, or in this case not achievable. Correspondence to: Dr Ron Borland, Cancer Council Victoria, 615 St Kilda Rd, Melbourne, VIC 3004; e-mail: [email protected]
Australian and New Zealand Journal of Public Health © 2015 Public Health Association of Australia
115
