Quantifying the value of stroke disability outcomes: WHO global burden of disease project disability weights for each level of the modified Rankin Scale.

BACKGROUND AND PURPOSE

The modified Rankin Scale (mRS) categorizes poststroke disability among 7 broad, ordinal grades, but the interval distances between these levels are spaced along the disability spectrum have not been previously investigated.

METHODS

We used the person trade-off procedure developed by the World Health Organization Global Burden of Disease Project (WHO-GBDP) to generate disability weights (DWs) ranging from 0 (normal) to 1 (dead) for each of 7 mRS grades. The ratings of an international, 9-member panel of stroke experts were combined by a modified Delphi process.

RESULTS

DWs (95% CI) were 0 for mRS 0, 0.046 (0.004 to 0.088) for mRS 1, 0.212 (0.175 to 0.250) for mRS 2, 0.331 (0.292 to 0.371) for mRS 3, 0.652 (0.625 to 0.678) for mRS 4, 0.944 (0.873 to 1.015) for mRS 5, and 1.0 for mRS 6. DWs of adjacent mRS levels were significantly different (P<0.001 for all). Coefficients of variation showed a high degree of consensus for DWs among panel members. DWs placed each of the 5 intermediate mRS states in different disability class levels of the WHO-GBDP anchor conditions and identified natural clusters to use when reducing the mRS to fewer categories.

CONCLUSIONS

Formal DW assignment confirms that the mRS is an ordered but unequally spaced scale. The availability of DWs for each mRS level now permits direct comparison of each poststroke outcome state with the outcomes of hundreds of other diseases in the WHO-GBDP and the expression of stroke burden in different populations by using the uniform metric of disability-adjusted life-years lost.