title: A simple, assumption-free, and clinically interpretable approach for analysis of modified Rankin outcomes.
abstract: OBJECTIVE
  There is debate regarding the approach for analysis of modified Rankin scale scores, the most common functional outcome scale used in acute stroke trials.
  
  
  METHODS
  We propose to use tests to assess treatment differences addressing the metric, "if a patient is chosen at random from each treatment group and if they have different outcomes, what is the chance the patient who received the investigational treatment will have a better outcome than will the patient receiving the standard treatment?" This approach has an associated statement of treatment efficacy easily understood by patients and clinicians, and leads to statistical testing of treatment differences by tests closely related to the Mann-Whitney U test (Wilcoxon Rank-Sum test), which can be tested precisely by permutation tests (randomization tests).
  
  
  RESULTS
  We show that a permutation test is as powerful as are other approaches assessing ordinal outcomes of the modified Rankin scores, and we provide data from several examples contrasting alternative approaches.
  
  
  CONCLUSIONS
  Whereas many approaches to analysis of modified Rankin scores outcomes have generally similar statistical performance, this proposed approach: captures information from the ordinal scale, provides a powerful clinical interpretation understood by both patients and clinicians, has power at least equivalent to other ordinal approaches, avoids assumptions in the parameterization, and provides an interpretable parameter based on the same foundation as the calculation of the probability value.
authors.affiliation: Department of Biostatistics, University of Alabama at Birmingham School of Public Health; Birmingham, AL 35294, USA. ghoward@uab.edu
authors.forename: George
authors.initials: G
authors.lastname: Howard
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Waller
authors.forename: Jenifer H
authors.initials: JH
authors.lastname: Voeks
authors.forename: Virginia J
authors.initials: VJ
authors.lastname: Howard
authors.forename: Edward C
authors.initials: EC
authors.lastname: Jauch
authors.forename: Kennedy R
authors.initials: KR
authors.lastname: Lees
authors.forename: Fenwick T
authors.initials: FT
authors.lastname: Nichols
authors.forename: Volker W
authors.initials: VW
authors.lastname: Rahlfs
authors.forename: David C
authors.initials: DC
authors.lastname: Hess
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D016017:Odds Ratio; D017063:Outcome Assessment, Health Care / Q000379:methods*; D011336:Probability; D016016:Proportional Hazards Models; D015203:Reproducibility of Results; D012107:Research Design; D020521:Stroke / Q000628:therapy*; D016896:Treatment Outcome