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Objective - This paper presents alternative health externalities quantification methods in the context of a randomised controlled trial comparing family therapy with treatment as usual as an intervention for self-harming adolescents, and discusses the practical limitations of those methods.
Methods - The trial followed a sample of 754 participants aged 11 to 17 years. Health utilities are measured using answers to EQ-5D-3L for the adolescent and to HUI2 for one parent at baseline, 6 and 12 months. We use regression analyses to evaluate the association between parent's and adolescent's health utilities, controlling for additional health assessment for the adolescent, type and number of self-harm events as well as variables for both the adolescent and the parent. Cost-effectiveness over a 12-month period is presented using mean incremental cost-effectiveness ratios.
Results - We find that the parent's health utility increased over the duration of the trial and is significantly and positively associated with adolescent's health utility at 6 and 12 months only. When considering adolescents' health gain only, the ICER is £45,330 per QALY. When including health externalities to one parent, the ICERs estimates range from £33,690 per QALY to £45,330 per QALY and can also be a dominated option depending on the quantification method used.
Conclusion - We argue that the use of a single disutility value for any parent denies the heterogeneity observed in parents of self-harming adolescents and ignores the QALY gain of parents over the duration of the trial. We demonstrate how adding QALY gains for both the adolescent and the parent might also lead to a dilemma of judging an intervention cost-effective when it benefits the rest of the family but not the patient. We finally propose the use of a household welfare function along with an equivalence scale to measure health externalities for cost-effectiveness analysis.
