Issues in evaluating the costs and cost-effectiveness of Cognitive Behavioural Therapy for overweight/obese adolescents, CHERE Working Paper 2009/1

Economic evaluation is the systematic assessment of the costs and consequences of alternative courses of action. In health and healthcare, the results can be used to inform clinicians and policy makers about the relative cost-effectiveness of options under consideration [1]. Many economic evaluations are undertaken alongside randomised controlled trials (RCTs); the advantages of this approach are that i) prospective, accurate data can be collected on costs and effects and ii) appropriate outcome measures for use in economic evaluation can be chosen. The outcome of an economic evaluation is usually described as a ratio of the costs and effects ? often called the incremental cost-effectiveness ratio (ICER). The ICER is determined by calculating the differences in the costs and effects of both intervention and control groups and dividing the former by the latter. In designing an economic evaluation, the important questions to resolve are: which costs should be included and which outcome measures are most appropriate for estimating the cost-effectiveness ratio? In 2005, the Australian Technology Network of Universities funded the Centre for Metabolic Fitness (CMF) through a competitive, peer-reviewed process. The aims of the centre are to develop and evaluate diet and exercise interventions to counteract metabolic syndrome and assess their acceptability by target community groups. Metabolic syndrome is a cluster of metabolically determined risk factors associated with obesity (e.g. hypertension, impaired blood glucose etc). A number of collaborative projects have been developed within the centre, one of which is the CHOOSE HEALTH project. As part of this project, the effectiveness of cognitive behavioural therapy (CBT) as an intervention for overweight or obese adolescents has been trialled at the University of RMIT by Leah Brennan and the University of South Australia by Margarita Tsiros, as part of their post-graduate studies1. Subsequently, it has been decided to add an economic component to this work. Trials of the effectiveness and cost-effectiveness of different means of delivering cognitive behaviourally based weight management programs are planned2. This paper reports the results of investigations into the two questions which need to be addressed prior to undertaking a formal economic evaluation of the CHOOSE HEALTH program: i) what costs should be included and ii) which measures of outcome are suitable for estimating an ICER in this context. The paper is organised in four sections. Following the introduction (section 1) and brief descriptions of the background to and context in which the program was planned (section 2), details of the RMIT trial design and results are provided in section 3. In the final section (section 4), a cost model is presented and the implications of the outcomes used in the initial trials of the effectiveness are discussed in relation to designing a prospective economic evaluation of the CHOOSE HEALTH program.