Appendix

Cost calculations

Direct medical and non-medical costs of DMD

Direct medical and non-medical costs of DMD were calculated using data on resource use and national reference prices[1-3]. Costs for medical aids and devices were obtained through input from experts within the Translational Research in Europe – Assessment and Treatment of Neuromuscular Diseases (TREAT-NMD) network.

Indirect cost of DMD

Indirect costs of DMD were quantified in accordance with the human capital approach, in which the societal loss in production is valued at the cost of employment (i.e. the national mean gross income plus employer’s costs and social fees [4,5]). The annual number of hours of lost production for caregivers were calculated using information on work status, type of employment (e.g. full-time or part-time), number of work hours per week, if they had reduced their working hours or stopped working completely because of their sons’ DMD, and the number of hours they were paid to provide informal care. We also calculated production losses associated with absenteeism and reduced productivity while working using outcomes from the Work Productivity and Activity Impairment Questionnaire (WPAI) [6] and the reported number of hours worked (excluding paid formal care). The annual number of hours of lost production for patients≥18 years of age not employed or in full-time education was estimated using data on the national mean number of hours working per year (for those who were employed) from the Organisation for Economic Co-operation and Development (OECD) [7].

Informal care costs

We valued each hour of paid informal care as reported by the caregivers according to the human capital approach at the cost of employment (described above). Unpaid informal care was quantified as the number of hours of leisure time devoted to informal care. To avoid double-counting costs of care provided via nurse visits to the home, personal assistants, etc.,and to allow for an unadjusted estimation of indirect costs in accordance with the human capital approach, we estimated the number of hours devoted to informal caregiving using outcomes from the WPAI and data from OECD on the mean daily number of hours of leisure time for an adult in the UK general population [7]. Each hour of leisure time was then conservatively valued at 35% of the country-specific national mean gross wage, in line with previous research and recently updated estimates of the value of travel time savings [8,9].

Targeted review of the literature

We developed a search strategy to identify input data concerning life expectancy in DMD, time to ventilation support in DMD, costs of DMD in the UK, and health-related quality of life (in terms of utilities) in patients with DMD in the UK and their caregivers, as well as previous economic models of treatments for DMD. The searches were performed in PubMed and Web of Science. To reflect current treatment practices, only articles published after 2005 were considered. The applied search terms are provided in eTable 1.

eTable1: Targeted literature review search terms

Concept / Search terms
Duchenne muscular dystrophy / “Muscular Dystrophy, Duchenne”[Mesh]
Life expectancy / “Mortality”[Mesh]
“Survival”[Mesh]
“Life Expectancy”[Majr]
Ventilation support / “Respiratory Insufficiency”[Mesh]
“Respiratory Mechanics/physiology”[Mesh]
Cost of illness / “Costs and Cost Analysis”[Mesh]
“Cost of Illness”[Mesh]
Quality of life / “Quality of Life”[Majr]
“Utilities”
“Utility”
Economic models/evaluations / “Cost-Benefit Analysis”[Mesh]

One-way deterministic sensitivity analysis results

eFigure1: One-way deterministic sensitivity analysis of model I (parameters altered ±50%)

Note: Bars for utility input were truncated as these data were limited at 0 and 1, respectively.The bar for discount rate costs appears truncated as both the lower (-50%) and higher (+50%) value generated a lower ICER.

eFigure2: One-way deterministic sensitivity analysis of model II (parameters altered ±50%)

Note: Bars for utility input were truncated as these data were limited at 0 and 1, respectively. EA=Early ambulatory. LA=Late ambulatory. ENA=Early non-ambulatory. LNA=Late non-ambulatory.

eFigure3: One-way deterministic sensitivity analysis of Model III (parameters altered ±50%)

Note: Bars for utility input were truncated as these data were limited at 0 and 1, respectively.

References

1British National Formulary (BNF). British Medical Association and the Royal Pharmaceutical Society. Available at: (accessed October 15, 2012).

2Department of Health. National schedule of reference costs 2010–11 for NHS trusts. Available at: http://www.dh.gov.uk/prod_consum_dh/groups/dh_digitalassets/documents/digitalasset/dh_131145.xls (accessed November 19, 2012).

3Personal Social Services Research Unit (PSSRU). Unit costs of health & social care 2011. Available at: (accessed October 15, 2012).

4Drummond M, Sculpher M, Torrance G, et al. Methods for economic evaluation of health care programmes (3rd Edition). Oxford: Oxford University Press; 2005.

5Kobelt G. Health Economics: An Introduction to Economic Evaluation (2nd Edition). London: Office of Health Economics; 2002.

6Reilly MC, Zbrozek AS, Dukes EM. The validity and reproducibility of a work productivity and activity impairment instrument. Pharmacoeconomics 1993;4:353-365

7The Organisation for Economic Co-operation and Development (OECD). Work-life balance. Available at: (accessed August 28, 2012).

8Johannesson M, Borgquist L, Jonsson B, Rastam L. The costs of treating hypertension: an analysis of different cutoff points. Health Policy 1991;18:141-150.

9United States Department of Transportation. The value of travel time savings: departmental guidance for conducting economic evaluations, revision 2 (2011). Available at: http://www.dot.gov/sites/dot.dev/files/docs/vot_guidance_092811c.pdf (accessed March 25, 2013).