We appreciate Dalziel and Segal's interest in our article, “Economic Analysis of a School-Based Obesity Prevention Program” (1). We also appreciate the opportunity to respond to their comments. Their critique of our analysis focused mainly on 4 issues: 1) lack of evidence concerning program participants’ weight after the 2-year intervention period; 2) lack of good data linking being overweight as a child with being overweight as an adult; 3) intervention participants who were considered in the evaluation; and 4) our use of estimated downstream medical costs associated with overweight/obesity at age 40 to 65 years. We appreciate the authors’ concerns but do not agree with many of their comments or with the alternative assumptions they made in their own analysis.
The first issue was clearly acknowledged in our article. Dalziel and Segal made an important point that relapse rate should be incorporated in cost effectiveness analysis of childhood obesity prevention programs. We did not incorporate a relapse rate in our analysis because the randomized control trial of the Planet Health program did not assess the overweight relapse rate after the 2-year intervention, and there are limited data on long-term outcomes of childhood obesity prevention programs. To be relevant to our analysis, relapse information would need to come from trials of childhood obesity prevention interventions similar to the Planet Health program. In the existing literature, we have not found such a study. In their analysis, Dalziel and Segal assumed that 50% of previously overweight program participants who achieved normal weight status during the intervention would relapse to overweight status by year 7. However, they did not provide any justification for their assumption of a 50% relapse rate. Incorporating any relapse rate into the model will obviously decrease the estimated cost effectiveness of the program, but this more conservative result is not necessarily more appropriate or accurate unless there is sound justification for the assumed rate of relapse. Future intervention studies of childhood obesity prevention programs should include long-term outcome evaluations to accurately assess relapse rates.
We also agree with Dalziel and Segal's concern about using historical data to estimate the probability of overweight children becoming overweight adults, given the recent rapid increase in the prevalence of overweight and obesity. Because long-term follow-up data tracking overweight from childhood to adulthood are limited, we had to rely on the only data that were available when we conducted our study. We acknowledged this as a limitation in our article. In their critique, Dalziel and Segal stated that they used “alternative assumptions to the four main limitations,” but no alternative assumption addressed this concern.
The third issue raised by Dalziel and Segal actually reflects a misunderstanding of our study design. Our economic analysis of the Planet Health program was based on the costs and effectiveness of the program as a whole. In estimating intervention costs, we considered the costs for all participants, not just the female students. Because the change in overweight prevalence among male students was not statistically significant, we assumed zero intervention impact on male students. Therefore, in assessing intervention effectiveness, the number of overweight adults prevented among female students was considered to be the total number of overweight adults prevented by the intervention. In their alternative analysis, Dalziel and Segal averaged the change in overweight prevalence among males and females. This method takes into account a small increase in male overweight prevalence, which, in fact, was not statistically significant. Therefore, their recalculation of intervention effectiveness was unwarranted.
The last issue raised involves our decision to include downstream medical costs in our analysis. Dalziel and Segal argued that “given that this is 30 to 50 years in the future, the confidence that can be placed on these estimates is low.” Their alternative assumption was to exclude all medical cost savings associated with the prevention of adult overweight. We do not agree with this assumption. First, it is a common practice to include estimates of future direct medical costs in cost-effectiveness analyses. Excluding such estimated costs in our evaluation of the Planet Health program would make it difficult to compare the cost-effectiveness results of our study with those of similar studies. Second, both quality adjusted life years (QALYs) gained and medical cost savings associated with the prevention of overweight in adulthood are downstream benefits of the intervention. Because the medical costs are downstream costs, we not only discounted them to age 14 years, we also performed a sensitivity analysis within a plausible range. Obviously, excluding downstream medical costs will reduce the estimated cost effectiveness of this intervention. However, such an approach is neither appropriate nor realistic but reflects an overly conservative assumption that the intervention will have no effect on participants’ future medical costs.
The analysis presented by Dalziel and Segal is based on alternative assumptions that were either unnecessary, without justification, or extremely conservative. However, their finding of $33,456 per QALY gained would still be considered by many policy-makers as cost effective (2).