The cost-effectiveness of physical activity interventions in adolescents: model development and illustration using two exemplar interventions

Objective: To develop a model to assess the long-term costs and health outcomes of physical activity interventions targeting adolescents. 
Design: A Markov cohort simulation model was constructed with the intention of being capable of estimating long-term costs and health impacts of changes in activity levels during adolescence. The model parameters were informed by published literature and the analysis took a National Health Service perspective over a lifetime horizon. Univariate and probabilistic sensitivity analyses were undertaken. 
Setting: School and community 
Participants: A hypothetical cohort of adolescents aged 16 years at baseline. 
Interventions: Two exemplar school-based: a comparatively simple, after-school intervention and a more complex multi-component intervention compared to usual care. 
Primary and secondary outcome measures: Incremental cost-effectiveness ratio as measured by cost per quality-adjusted life year gained. 
Results: The model gave plausible estimates of the long-term effect of changes in physical activity. The use of two exemplar interventions suggests that the model could potentially be used to evaluate a number of different physical activity interventions in adolescents. The key model driver was the degree to which intervention effects were maintained over time. 
Conclusions: The model developed here has the potential to assess long-term value for money of physical activity interventions in adolescents. The two applications of the model indicate that complex interventions may not necessarily be the ones considered the most cost-effective when longer-term costs and consequences are taken into account.