Parental Health Spillover in Cost-Effectiveness Analysis: Evidence from Self-Harming Adolescents in England.

OBJECTIVE: This article presents alternative parental health spillover 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 11-17 years. Health utilities are measured using answers to the EuroQoL 5 Dimensions 3 Levels (EQ-5D-3L) for the adolescent and the Health Utility Index (HUI2) for one parent at baseline, 6 and 12 months. We use regression analyses to evaluate the association between the parent's and adolescent's health utilities as part of an explanatory regression model including health-related and demographic characteristics of both the adolescent and the parent. We then measure cost-effectiveness over a 12-month period as mean incremental cost-effectiveness ratios using various spillover quantification methods. We propose an original quantification based on the use of a household welfare function along with an equivalence scale to generate a health gain within the family to be added to the adolescent's quality-adjusted life-year gain.

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 but not at baseline. When considering the adolescent's health gain only, the incremental cost-effectiveness ratio is £40,453 per quality-adjusted life-year. When including the health spillover to one parent, the incremental cost-effectiveness ratio estimates range from £27,167 per quality-adjusted life-year to £40,838 per quality-adjusted life-year and can be a dominated option depending on the quantification method used.

CONCLUSION: According to the health spillover quantification method considered, the incremental cost-effectiveness ratios vary from within the National Institute for Health and Care Excellence (NICE) cost-effectiveness threshold range to not being cost-effective.