The Cost-Effectiveness of Individual Cognitive Behaviour Therapy for Overweight / Obese Adolescents

Transcription

1 Dr Marion HAAS R Norman 1, J Walkley 2, L Brennan 2, M Haas 1. 1 Centre for Health Economics Research and Evaluation, University of Technology, Sydney. 2 School of Medical Sciences, RMIT University, Melbourne. The Cost-Effectiveness of Individual Cognitive Behaviour Therapy for Overweight / Obese Adolescents Slide 1*: Evaluating the cost-effectiveness of Cognitive Behavioural Therapy for Overweight/Obese Adolescents Slide 2: Economic evaluation is the systematic assessment of the costs and consequences of alternative courses of action. The results can be used to inform clinicians and policy makers about the relative cost-effectiveness of options under consideration. Many economic evaluations are undertaken alongside RCTs; the advantages of this approach are 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 typically presented as a ratio of the costs and effects often called the incremental cost-effectiveness ratio (ICER). The ICER is calculated by calculating the differences in the costs and effects of both intervention and control groups and dividing one by the other. 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? Slide 3: In 2005, the Australian Technology Network of Universities funded the Centre for Metabolic Fitness. 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 is metabolically determined risk factors associated with obesity (ie hypertension, impaired blood glucose etc). A number of collaborative projects have been developed within the centre, one of which is the Choose Health project. The effectiveness of CBT as an intervention for overweight or obese adolescents has been trialled at both RMIT and UniSA by two PG students, Leah Brennan and Margarita Tsiros. It has been decided to add an economic component to this work by including an economic evaluation alongside future trials of the Choose Health project. To prepare the ground for such work, we have developed a cost model of the Choose Health program and undertaken an exploration of the issues we are likely to confront in a trial evaluation of the costeffectiveness of Choose Health. Slide 4: Why overweight and obese adolescents? There is concern about the increase in overweight and obesity amongst children in Australia. Experts have agreed the following: BMI measurement in children and young people should provide age- and gender-specific information eg BMI-for-age z score. Tailored clinical intervention should be considered for children with a BMI at or above the 91st percentile, depending on the needs of the individual child and family. Assessment of co-morbidity should be considered for children with a BMI at or above the 98th percentile.

2 Slide 5: why Cognitive Behavioural therapy (CBT)? Behavioural therapy and CBT incorporating changes to dietary and exercise behaviour have been shown to result in greater weight loss than regular diet and exercise interventions. In addition, recent improvements in the CBT model are expected to result in better maintenance of weight loss also. CBT can be used successfully in a range of settings, in either individual or group mode and can be delivered by a range of health professionals. Slide 6: Choose Health is the name given to a program incorporating CBT which was developed initially at RMIT by Leah Brennan and Jeff Walkley and trialled by Leah for her PhD. The specific aim of the program is to produce a weight loss of between 5% and 10% which is maintained over a specified period of time, largely by mediating the biological outcomes of overweight or obesity. Other aims include improving behavioural habits around eating and physical activity, reducing disordered eating and improving psychosocial functioning. Slide 7: The original Choose Health program designed by Leah and Jeff consisted of 12 sessions plus some follow-up sessions; two clinic sessions and eight phone calls. An initial trial was conducted with 63 overweight or obese adolescents. The results indicated that the intervention improved self-reported eating behaviour, physical activity and sedentary activity outcomes as well as laboratory measured fitness and body composition outcomes. Slide 8: In this trial, CBT alone was compared with CBT preceded by motivational interviewing (MI), a technique developed in the treatment of alcoholism and now used widely in the drug and alcohol field, aims to assist the individual to become ready for change. MI has been used in conjunction with CBT to increase treatment initiation and completion rates and to improve treatment outcomes; however, the use of MI in the treatment of overweight and obesity has received very little attention in the theoretical and empirical literature.the more important comparator for the economic evaluation was a waiting list for CBT the adolescents in this control group received no CBT initially. Slide 9: This diagram illustrates the design of the trial undertaken by Leah. Potential participants and their families were recruited by advertisement. MI is Motivational Interviewing, described above.

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4 Slide 10: An example of the results of the effectiveness analysis is illustrated in this table. BMI-for-age z score is a measure of the standard deviation away from aged standardised mean weights. It is considered one of the most appropriate measures of weight in children and adolescents because it accounts for the wide, natural variation in growth. The results for this measure show that pre-treatment, the weight of participants in the treatment and control groups was similar, although overall and for girls, the treatment group was less overweight than the control. Following the intervention, the results show that the treatment group lost more weight than the control group; the BMI-for-age Z score for the treatment group fell by 0.13 while the control group gained The pattern is repeated for both girls and boys. Overall, the BMI-for-age z score and BMI were statistically significantly different, but the BMI percentile was not significant.

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6 Slide 11: To interpret BMI-for-age z scores, we need to understand that 0= normal weight. The NICE guideline on obesity indicates that the 91st and 98th percentile were the cut-offs for overweight and obesity, respectively. If we assume a normal distribution, the 91st percentile is 1.34 standard deviations from the mean, and the 98th percentile is Therefore, the children in this trial were generally obese under this classification at the start, and remain so after the intervention, albeit at a lower z-score. Slide 12: Treatment resulted in improved body composition at post treatment and sustained or improved body composition following maintenance. Despite reductions in weight and body fat, lean body mass was not affected by the intervention, thus, treatment did not detrimentally effect linear growth and lean body tissue. Participation in a motivational interview prior to this cognitive behavioural intervention did not influence treatment outcomes. Of note, BMI based weight classification systems recommended for research and clinical practice did not consistently classify adolescent overweight and obesity, and, weight classification based on BMI criteria was a poor indicator of percent body fat, particularly in males. Slide 13: The cost of a Choose Health program (12 sessions) is shown below. In the table, research-specific costs are presented in italics. The costs are based on a salary for a Psychologist, Grade 3, Year 2. On-costs of 30% have been included and time for preparation has been allowed for. In a non-research setting, the Choose Health program would cost just under $890 per participant. The cost for MI was essentially the same as for CBT. Those randomised to CBT received either an assessment interview or an MI. so in this instance MI acted as a comparator. As mentioned previously, for the purposes of the economic evaluation, the control group was a waiting list for CBT. Costs of CBT for obesity in adolescents Period Cost Item Unit Cost Total (Italic if research setting only) Intake 15 minute questionnaire (research setting only) $49.92 p/h $12.48 Assessment Assessment interview (1 hour) $49.92 p/h $49.92 Printing (12 pages) $0.05 per sheet $0.60 Monitoring instructions (30 minutes) (research setting only) $49.92 p/h $24.96 Treatment 12 sessions (1 hour per session) $49.92 p/h $ Maintenance 2 sessions (1 hour) $49.92 p/h $ phone calls (15 minutes) $49.92 p/h $99.84 $ ($886.68) Assumption that contacts are with a public psychologist Grade 3, Year 2. On-costs of 30% have been added and includes a period of preparation time for each consultation. Slide 14: Using the results for both costs and effects, we should in theory, be able to calculate an ICER. However, in this case, an ICER such as the cost per unit decrease in z score ($7718= 849/0.11) is clearly neither a sensible nor useful result because an ICER is only useful in a relative sense ie if we can compare it with a result from another study. This requires the use of the same measure/s of outcome understanding this issue makes it clear why lives saved, life-years saved and QALYs are such popular outcome measures they allow the comparison of ICERs across different interventions or programs. The use of ICERs also requires that a threshold be set a cost/outcome that indicates society s willingness to pay. It is rare for such threshold to be explicit but an examination of a set of decisions (eg PBAC decisions to list new medicines) provides an indication that the current threshold in Australia is somewhere in the vicinity of $70,000-$80,000 per QALY gained.

7 Slide 15: There is clearly still some additional work to be done to establish the effectiveness of Choose Health more rigorously. The work that has been done to date has involved a small number of participants, short term follow-up and has only trialled a one-to-one intervention. Slide 16: Similarly, there is a lot more work to be done on the cost side of the equation. In the short run, as we have shown, CBT for overweight or obesity in adolescents is likely to be expensive for a number of reasons. It is usually delivered as an individual intervention or in very small groups. There are large time demands on the health professional we calculated that each participant received 16 hours of contact time plus preparation time. Slide 17: Short term costs may be reduced by the use of group therapy. If a similar outcome can be achieved, then the cost per child will fall in proportion to the group. For example, if three children participate in all treatment and maintenance sessions, the cost per child falls to $383. While it may be cheaper to offer the program in a group format, this may not deliver the same level of benefits; adolescents are very concerned that others will find out that they are attending a 'fat group' and it may be counterproductive to increase their anxiety about this, or put them at risk of being teased as a result of attending. It is also considered that one of the important components of the program is its emphasis on the parent-adolescent partnerships. This would be very difficult to create in a group setting, and in fact research suggests that for group work it is more effective to see adolescents and parents separately. There will also be savings if less qualified staff are used to deliver the intervention. So far, CBT has only been trialled in obesity interventions using highly qualified practitioners. Research has shown that, with appropriate training and supervision, non-psychologists such as diabetes educators, nutritionists and nurses can effectively deliver cognitive behavioural interventions. But the value for money will only be maintained if similar outcomes are achieved to those observed in the original Choose Health program. Slide 18: The short term analysis of the costs and effects of Choose Health probably makes CBT for overweight and obesity appear less effective than it is. We can identify those who respond positively to the program but we fail to capture the full effects of the program as long term outcomes in terms of maintained weight loss are not available. Levels of morbidity and mortality in adolescence are relatively small and we are not able to capture any long term effects of weight loss on these outcomes. In the long term, we might expect some compensating cost outcomes. For example, fewer working days may be lost to obesity-related conditions, medical expenditure may be reduced and food expenditure may change (although healthy eating may be more expensive in terms of the types of food, if less food overall is consumed, overall costs may be lower). However, generating the data to enable such estimations to be made requires complex and highly uncertain data modelling. Slide 19: How can we overcome these barriers? Short term data is always going to be the most reliable but they are unlikely to capture either the true costs or outcomes. One solution is to undertake long term follow-up of trial participants. However, as this is likely to have to extend over decades rather than years, it is probably unrealistic. The most likely means we have at our disposal is to model the data. However, we are not able to do this currently, as the evidence which would enable us to make the links between i) intervention and behaviour change (ie reduced consumption, increased physical activity), ii) behaviour change and changes in weight and iii) changes in weight, health-related quality of life, utility, long term morbidity and mortality, does not exist.

8 Slide 20: In conclusion, economic evaluation is a useful tool for providing clinical and policy relevant information about the extent to which alternative interventions, programs or services represents value for money. However, as this presentation has demonstrated, it is of limited usefulness where the evidence is lacking in terms of long term outcomes. If we cannot report the cost per life year saved or per QALY gained for CBT for adolescent obesity, then we are not able to judge its relative cost effectiveness compared to either other obesity interventions, other interventions targeting the health of adolescents or other interventions more generally. * Note: This paper is in the format of slide notes to accompany the associated PowerPoint presentation accessed via the links menu under the author s name.