Page 29 - Go4it

never a problem to 4 = almost always a problem). Scales are standardized, and scores range from 0-100, with higher scores representing better quality of life. The PedsQL has been shown to be both reliable and valid (33,34).
- Body Esteem Scale for Adolescents and Adults
The Body Esteem Scale (BES) questionnaire for adolescents has 3 subscales: BES-Appearance (general feelings about appearance), BES-Weight (weight satisfaction), and BES-Attribution (evaluations attributed to others about one’s body and appearance). The subscales have high internal consistency and 3- months test-retest reliability (35).
Statistical analyses
Descriptive statistics (means±SD or median and interquartile ranges, as appropriate) will be used to describe the study sample with regard to baseline characteristics. To evaluate the effects of the intervention, longitudinal linear and logistic regression analysis will be used. The mean difference between intervention and control group with 95% confidence intervals will be calculated. Regression analyses will be adjusted for baseline values and possible confounders such as gender and age. Also, effect modification will be investigated using interaction terms between intervention group and gender and age, respectively. All analyses will be performed according to the intention-to- treat-principle, meaning that we will not impute values for missing data (36).
Economic evaluation
An economic evaluation will be conducted from a societal perspective. All relevant costs will be assessed, valued and analysed. Costs will include costs of the interventions (Go4it programme and usual care), but also other health care related costs. For example, costs of visits to general practitioners, psychologists, physiotherapists, dieticians, paediatricians will also be estimated as well as costs of medication. Indirect costs of production loss are not relevant to this population of teenagers. Relevant cost data will be collected through cost diaries (37). Costs will be valued according to guidelines for economic evaluation in the Netherlands. Primary outcomes in the economic evaluation will be quality of life, BMI, physical activity and dietary behaviour. The economic evaluation will be performed according to the intention-to-treat principle. A cost-effectiveness analysis will be performed. The mean differences in total costs between intervention groups will be estimated and bootstrapping will be used to estimate 95% confidence intervals. Cost-effectiveness ratios will be estimated using bootstrapping techniques and graphically presented on cost-effectiveness planes. The incremental cost-effectiveness ratio expresses the additional costs of the Go4it programme per unit improvement of the effect. Acceptability curves will also be presented in which the probability that the programme is cost- effective is expressed as a function of willingness-to-pay.
Study design
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