An intensive tobacco dependence intervention based on SDT that targeted all smokers, not only those who wanted to stop within 30 days, was found to be cost-effective compared with other services commonly covered by health plans, including less intensive tobacco dependence treatment and prevention, as well as other medical services. Remarkably, the overall incremental cost-effectiveness ratio was about $1300 per QALY. Indeed, these findings were based on intention-to-treat data and thus may be conservative estimates. Further, unlike in actual practice, all CC participants in this study were offered a low-intensity intervention. Sensitivity analyses indicated that using: (1) generic medications, (2) biochemically validated tobacco abstinence, (3) actual rates of tobacco abstinence for each gender and age group, (4) life-years saved (not adjusted for quality of life), and (5) costs in 2011 US dollars yielded only small changes in cost per QALY, suggesting that our findings were robust to several plausible variations in the model parameters.
These findings support adoption of intensive tobacco dependence interventions by the US healthcare system for all smokers who are willing to discuss their tobacco use, as the SDT-based intervention was cost-effective even for those who did not want to stop within 30 days. Although the intervention was provided by a tobacco dependence treatment team, it was integrated with cardiovascular risk information typically discussed in primary care settings, and about half of the participants who used medications received them from their own healthcare provider. Thus, it is feasible for primary care providers to deliver the intervention to smokers who are willing to receive intensive treatment, although we note that within the scope of this study we were not able to measure all costs associated with this form of delivery. Alternatively, a health-care system could employ counselors at a central location with which primary care providers could collaborate to provide the intervention.
Herein, and in other published articles from this trial, we have emphasized the importance of demonstrating that theoretically consistent mechanisms of change explain the effect of the intervention in facilitating long-term tobacco abstinence. Previous findings from this trial have shown that the intervention was effective in enhancing patient autonomy and perceived competence, and thus consistent with the SDT model of health-behavior change.14
Interventions, no matter how intensive, that do not address these fundamental aspects of motivation may not yield comparable cost-effectiveness estimates. The proposed explanatory constructs derived from SDT—autonomy and perceived competence—are wholly consistent with the principles of biomedical ethics. Although a focus on mediators of treatment effects is relatively rare among cost-effective interventions, its importance is not to be missed. For instance, if the intervention facilitated tobacco abstinence but undermined patient autonomy, it would not be suitable for translation into medical practice because support for patient autonomy is an outcome that is equivalent to improving patient well-being.15,25
That cost-effective interventions support patient autonomy ought to be a benchmark standard for future comparative effectiveness trials and value-based medical studies to attain.26
Several limitations deserve mention. First, the generalizability of our findings may be limited, as they were based on a single study with a modest sample size and participants who were recruited only from the greater Rochester, New York area. Second, medication costs were based on the self-reported amount of medication purchased, as we did not have the amount of medication consumed by each participant, and cost estimates for medications were obtained from the largest private insurer in the greater Rochester, New York, area. Third, we did not estimate the specific QALYs for our participants, but instead used published estimates of the effects of smoking cessation on quality of life and life expectancy within a nationally representative US sample stratified by gender and age.24
The full benefits of smoking cessation take many years to accrue and thus could not be directly derived from our study sample. Indeed, a recent study has demonstrated the improvement in quality of life for non-smokers and those who have stopped relative to those still smoking.27
Fourth, all participants who were lost to follow-up were assumed to be smoking, but this approach yields more, rather than less, conservative estimates, and modifications of relevant model parameters produced similar findings, thus underscoring the robustness of our findings. Future studies might focus on other areas of health-behavior change and evaluate cost-effectiveness based on QALYs for study participants.