The response rates at 6 months were 74.3%, 73.4%, and 74.9% for Web, PTC, and PTC-Web, respectively. Cessation rates among 6 month respondents were 41.4%, 46.9%, and 45.2%, respectively. On an intent-to-treat basis, with nonrespondents classified as smokers, the cessation rates were 30.7%, 34.3%, and 33.8%, respectively.
Intent-to-treat estimates (which involve use of all randomized study participants) commonly also assume all nonrespondents are smokers. To provide an estimate the cessation rate of nonrespondents, we imputed the probability of being a nonsmoker at 6 months for those individuals based on separate logistic regressions for each group. The dependent variables included smoking status at 21 days after planned quit date, smoking status at 12 weeks after planned quit date, cigarettes per day at baseline, motivation to quit, years of education, any previous quit of 6 months or longer duration, gender, age (and age squared), whether there was another smoker at home, whether the respondent was married, a depression index score, the Fagerstrom Test for Nicotine Dependence score, and body mass index. Including imputed probabilities of being a nonsmoker in the computation, the average 6 month cessation rates were 40.7%, 46.5%, and 45.2% for the Web, PTC, and PTC-Web groups, respectively. (These estimates are the expected values that would be obtained using multiple imputation [41
].) Thus, if imputed 6 month smoking status had been used instead of assuming individuals with missing data to be smokers, cost-effectiveness would have been 21.7%, 22.7%, and 22.1% greater, respectively. Prior research suggests that missing data imputation methods for inferring smoking cessation status are still subject to biases [42
Participants in the PTC and PTC-Web groups completed an average of 4.1 and 4.2 calls, respectively, while participants in the Web group completed 1.6 calls on average (including calls for additional support beyond the orientation call). Average call durations (in minutes) were: 14.4 Web, 67.8 PTC, and 72.4 PTC-Web. Logins averaged 5.7 and 3.4 for the Web and PTC-Web groups, respectively. Web use duration averaged 110.5 and 42.7 min for the Web and PTC-Web groups, respectively. However, the distribution of minutes on the Website was extremely skewed. Truncating at 250 min (the 95th percentile), Web use duration averaged 53.9, and 28.5 min for the Web and PTC-Web groups, respectively.
The LYs and QALYs saved following smoking cessation are shown Table , using the baseline scenario discount rate of 3%, as well as under discount rates of 0% and 5% (later used in the optimistic and pessimistic scenarios, respectively). The LYs saved varies by age, gender, and discount rate. At discount rates of 3% and 5%, there are generally fewer years saved at younger ages (mortality rates are low for both smokers and nonsmokers and future LYs saved are discounted) and at older ages (fewer LYs remain). With no discounting, LYs and QALYs are comparable for participants from 20 to 60 years old and decrease at older ages. Using the age and gender distribution of 6 month abstainers in our study and a 0% discount rate, the average LYs and QALYs are 6.17 and 5.51, respectively. Discounting by 3% reduces the average LYs and QALYs saved to 2.27 and 2.29, respectively. Discounting by 5% reduces the average LYs and QALYs saved to 1.22 and 1.35, respectively.
Life-years (LYs) and quality-adjusted life-years (QALYs) saved per lifetime quitter by gender and age of smoking cessation
The average number of LYs saved with a 0% discount rate that we calculated is similar to the 5.65 LY saved reported by Solberg et al. [43
], using data from the National Health Interview Survey and the National Mortality Feedback Survey for never, current, and former smokers (as compiled by Rogers and Powell-Griner [44
], a 14-year prospective study of 1.2 million US residents by Taylor et al. [45
], and the 2003 Behavioral Risk Factor Surveillance Study (BRFSS) [46
The cessation rates observed in this trial are comparable to those seen in phase 3 clinical trials of varenicline. The 6-month point prevalence rates for all treatment groups (30.7–34.3% before adjustment for biochemical validation) fall within the 95% CI for the abstinence rate estimated from currently available varenicline trials (28.9–37.8%) [1
Costs per nonsmoker in the baseline scenario are presented in Table . Cost per additional 6-month and additional lifetime quitter are similar across the three groups with the cost for the Web group being slightly lower. The cost per enrollee for the Web group ($373) was lower than the other two groups ($480 and $519), nevertheless the Web group was only modestly more cost effective ($2,601 per additional lifetime quitter versus $2,995 and $3,291 for the Web and PTC-Web groups, respectively), due to a marginally lower 6 month nonsmoking rate.
Cost-effectiveness with respect to 6 month and lifetime nonsmoking rates
Table also contains study results with respect to cost per LY and QALY saved under baseline assumptions. The cost per LY saved varied narrowly from $1,148 to $1,450 and the cost per QALY saved varied between $1,136 and $1,437. Upper and lower confidence limits on cost per QALY (based on corresponding confidence limits for the 6 month abstinence rate) vary from the point estimates by −20% to 31%.
The parameters used in developing pessimistic and optimistic scenarios for sensitivity analysis are shown in Table . The 6 month nonsmoking rates were set at the limits for the 95% confidence intervals; the spontaneous unaided yearly quit rates at 0.5% and 2.5% (relatively low and high values in the literature); the discount rates at 0% and 5% (two common values for sensitivity analyses); and other parameters at plus or minus 20% of the baseline values.
Parameters used in sensitivity analysis
The results for the pessimistic and optimistic scenarios are shown in Table . Under the pessimistic scenario (see upper half of Table ), the cost for each additional 6-month nonsmoker ranged from $1,810 to $2,264. The cost per additional lifetime quitter ranged from $4,423 to $5,532. The cost per LY saved ranged from $3,623 to $4,531 and the cost per QALY saved ranged from $3,274 to $4,095. Under the optimistic scenario (see lower half of Table ), the cost for each additional 6-month nonsmoker ranged from $887 to $1,132, and the cost per lifetime quitter ranged from $1,529 to $1,952. Cost per LY and QALY saved range from $278 to $354. There are only modest differences between groups in either the pessimistic or optimistic scenarios.
Cost-effectiveness using pessimistic and optimistic scenarios