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. 2015 Aug;46(8):2238-43.
doi: 10.1161/STROKEAHA.114.008547. Epub 2015 Jul 2.

Adopting a Patient-Centered Approach to Primary Outcome Analysis of Acute Stroke Trials Using a Utility-Weighted Modified Rankin Scale

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Adopting a Patient-Centered Approach to Primary Outcome Analysis of Acute Stroke Trials Using a Utility-Weighted Modified Rankin Scale

Napasri Chaisinanunkul et al. Stroke. .
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Background and purpose: Although the modified Rankin Scale (mRS) is the most commonly used primary end point in acute stroke trials, its power is limited when analyzed in dichotomized fashion and its indication of effect size challenging to interpret when analyzed ordinally. Weighting the 7 Rankin levels by utilities may improve scale interpretability while preserving statistical power.

Methods: A utility-weighted mRS (UW-mRS) was derived by averaging values from time-tradeoff (patient centered) and person-tradeoff (clinician centered) studies. The UW-mRS, standard ordinal mRS, and dichotomized mRS were applied to 11 trials or meta-analyses of acute stroke treatments, including lytic, endovascular reperfusion, blood pressure moderation, and hemicraniectomy interventions.

Results: Utility values were 1.0 for mRS level 0; 0.91 for mRS level 1; 0.76 for mRS level 2; 0.65 for mRS level 3; 0.33 for mRS level 4; 0 for mRS level 5; and 0 for mRS level 6. For trials with unidirectional treatment effects, the UW-mRS paralleled the ordinal mRS and outperformed dichotomous mRS analyses. Both the UW-mRS and the ordinal mRS were statistically significant in 6 of 8 unidirectional effect trials, whereas dichotomous analyses were statistically significant in 2 to 4 of 8. In bidirectional effect trials, both the UW-mRS and ordinal tests captured the divergent treatment effects by showing neutral results, whereas some dichotomized analyses showed positive results. Mean utility differences in trials with statistically significant positive results ranged from 0.026 to 0.249.

Conclusions: A UW-mRS performs similar to the standard ordinal mRS in detecting treatment effects in actual stroke trials and ensures the quantitative outcome is a valid reflection of patient-centered benefits.

Keywords: blood pressure; stroke; stroke management; thrombolysis.


Figure 1
Figure 1. Comparability of Utility Values for Modified Rankin Scale Levels
The utility weights derived from patient informants by the time tradeoff method (blue) and from healthcare provider informants by the person tradeoff method (red) are nearly identical, as consequently are their averaged values comprising the UW-mRS (green). Transitions from mRS health states 0-1, 1-2, and 2-3 are all valued moderately, from 3-4 and 4-5 valued more substantially, and from 5-6 not valued at all.
Figure 2
Figure 2
Trial Hypothesis Testing Using 5 Modes of Statistical Analysis of the Modified Rankin Scale P values are shown for trials using utility-weighting of the mRS, ordinal analysis of the mRS, and three dichotomized analyses of the mRS.

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