Stroke. 2007;38:1091-1096
Published online before print February 1, 2007,
doi: 10.1161/01.STR.0000258355.23810.c6
(Stroke. 2007;38:1091.)
© 2007 American Heart Association, Inc.
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Comments, Opinions, and Reviews |
Outcomes Validity and Reliability of the Modified Rankin Scale: Implications for Stroke Clinical Trials
A Literature Review and Synthesis
Jamie L. Banks, MSc, PhD
Charles A. Marotta, MD, PhD
From the Health Economics Research and Quality of Life Evaluation Services (J.L.B.), Abt Associates, Inc, Lexington, Mass; and Health Economics and Outcomes Research (C.A.M.), Division of Medical Sciences, AstraZeneca Pharmaceuticals LP, Wilmington, Del.
Correspondence to Charles A. Marotta, MD, PhD, AstraZeneca LP, 1800 Concord Pike, Wilmington, DE 19850. E-mail charles.marotta{at}astrazeneca.com
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Abstract
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Background and Purpose The modified Rankin scale (mRS),
a clinician-reported measure of global disability, is widely
applied for evaluating stroke patient outcomes and as an end
point in randomized clinical trials. Extensive evidence on the
validity of the mRS exists across a large but fragmented literature.
As new treatments for acute ischemic stroke are submitted for
agency approval, an appreciation of the mRSs attributes,
specifically its relationship to other stroke evaluation scales,
would be valuable for decision-makers to properly assess the
impact of a new drug on treatment paradigms. The purpose of
this report is to assemble and systematically assess the properties
of the mRS to provide decision-makers with pertinent evaluative
information.
Methods A Medline search was conducted to identify reports in the peer-reviewed medical literature (19572006) that provide information on the structure, validation, scoring, and psychometric properties of the mRS and its use in clinical trials. The selection of articles was based on defined criteria that included relevance, study design and use of appropriate statistical methods.
Results Of 224 articles identified by the literature search, 50 were selected for detailed assessment. Inter-rater reliability with the mRS is moderate and improves with structured interviews (
0.56 versus 0.78); strong test-re-test reliability (
=0.81 to 0.95) has been reported. Numerous studies demonstrate the construct validity of the mRS by its relationships to physiological indicators such as stroke type, lesion size, perfusion and neurological impairment. Convergent validity between the mRS and other disability scales is well documented. Patient comorbidities and socioeconomic factors should be considered in properly applying and interpreting the mRS. Recent analyses suggest that randomized clinical trials of acute stroke treatments may require a smaller sample size if the mRS is used as a primary end point rather than the Barthel Index.
Conclusions Multiple types of evidence attest to the validity and reliability of the mRS. The reported data support the view that the mRS is a valuable instrument for assessing the impact of new stroke treatments.
Key Words: cerebrovascular accident disability evaluation randomized controlled trials rankin scale reproducibility of results
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Introduction
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The modified Rankin Scale (mRS) is a clinician-reported measure
of global disability that has been widely applied for evaluating
recovery from stroke
1,2 and as a primary end point in randomized
clinical trials (RCTs) of emerging acute stroke treatments.
3 The value of the mRS as a RCT end point has been examined in
several investigations wherein proponents emphasize the importance
of the scales brevity, simplicity of use and interpretability
in the context of stroke trials.
4 Extensive evidence on the
validity, reliability and sensitivity of the mRS exists across
a broad but fragmented literature.
58
As new stroke drugs are submitted for agency approval, an in-depth understanding of the mRS in terms of its relationship to other stroke evaluation scales and clinical outcomes would be useful for decision-makers to properly assess their impact. The purpose of this review is to assemble and systematically assess the properties of the mRS to provide decision-makers with pertinent evaluative information they need for decision-making.
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Methods
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An initial literature search was conducted in MEDLINE from 1957
(date of original Rankin Scale (RS) publication to December
2004, with updates through April 2006) to identify articles
on (1) the structure, scoring, and psychometric properties of
the mRS and (2) the effectiveness of the mRS as an end point
in RCTs of acute stroke treatment. Search criteria included
the term Rankin AND one or more of each of the following MeSH
terms: psychometrics, reliability and validity, predictive value
of tests, sensitivity and specificity, disability evaluation,
statistics and randomized controlled trials. Other search terms
including lesion volume, stroke type, end point and design,
were used to search for additional articles. Two reviewers selected
articles for assessment based on relevance to the study objectives
and (1) the use of appropriate statistical methods in assessing
validity, and (2) analysis of the mRS as a primary end point
in RCTs of acute ischemic stroke treatments. The initial search
identified 224 articles of which 50 were selected for a detailed
assessment (40 relating mainly to validity/reliability, 2 to
the original Rankin and related scales, 8 related to RCTs).
Additional articles providing information on the limitations
of the mRS, and others were identified from bibliographies of
the retrieved articles.
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Results
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Historical Development
The history of the mRS dates from publication of the original
Rankin Scale in 1957.
1 Developed by Dr John Rankin in Glasgow,
Scotland, the RS comprises 5 grades of stroke severity ranging
from "no significant disability" to "severe disability" (
Table 1),
and was intended as a descriptive categorization of functional
recovery of cerebrovascular disease patients (>60 years)
at the time of discharge or transfer from the index hospitalization.
* The mRS was published in 1988 and consists of 6 categories (grades
0 to 5) rather than 5 for the RS; an additional category, grade
"6" denoting death, is usually incorporated into the mRS for
RCT purposes
9 (
Table 1). In the mRS: grade 1 of the original
RS ("no significant disability") is replaced by 2 grades, 0
and 1, with grade 0 describing patients without symptoms and
grade 1 describing patients without significant disability "despite
symptoms." This finer discrimination of mild strokes increases
the usefulness of the mRS in evaluating RCTs of acute stroke
interventions. Additionally, grade 2 in the mRS ("unable to
perform all previous activities") is more definitive compared
with that grade of the RS ("unable to carry out some of previous
activities").
The mRS is heavily weighted toward global disability (in particular, physical disability) and the need for assistance.2,6,7 As a global disability measure, the broad categories of the mRS (Table 1) subsume instrumental activities of daily living (IADL; eg, meal preparation, shopping, handling money)4 and basic ADLs (BADL; eg, walking, dressing, grooming) with emphasis on compromised motor function.10 The global nature of the mRS thereby allows the clinician to consider nonphysical attributes essential to a persons self-maintenance and well-being, such as cognition and language,4 social functioning,11 and poststroke mood disturbances, particularly depression, that may contribute to perceived disability.12 This allowance for consideration of IADLs and other nonphysical characteristics distinguishes the mRS from BADL-specific measures, such as the Barthel Index (BI).13
Test-Retest Reliability
Reliability refers to the extent to which a scale consistently and reproducibly measures the attributes it was intended to measure. Test-retest reliability evaluates the consistency of results over time in the absence of changes in the subject population and the raters.14 The
statistic indicates the extent of agreement among different sets of results not occurring by chance; a weighted
adjusts for the extent of disagreement, eg, differences of 1 grade versus 2 grades of the scale.
Strong test-re-test reliability of the mRS was reported in 2 independent studies (Table 2). In 1 investigation, 2 raters each graded 48 patients on 2 separate occasions with excellent consistency.15
Inter-Rater Reliability
Inter-rater reliability evaluates the consistency of results among raters. Because mRS categories are broad and the assessments are subjective, variability may occur across clinical raters. In 3 separate studies, inter-rater reliability of the mRS ranged from moderate to nearly perfect, indicated by the weighted
(Table 2). In addition to those studies, strong inter-rater reliability has also been reported for a German version of the mRS (
=0.76).16 Structured interviews have been shown to improve inter-rater reliability of the mRS.5,15,17 When used in a RCT setting, training and certification of raters should be considered to reduce inter-rater variability.
Validity
Validity is the degree to which an instrument measures the concept it was intended to measure. Construct validity is applied when a gold standard does not exist. This type of validity assessment uses multiple sources of comparison to test how accurately a measure captures the outcome it claims to measure in different contexts. Convergent (criterion) validity, a fundamental aspect of construct validity, measures the degree of correlation between different measures of the same construct. Other forms of validity include predictive validity (ability to predict future events)6,14 and theoretical validity (degree to which results are consistent with a priori expectations).18 In this report we focus on construct and convergent validity, clinical sensitivity and limitations, and then consider the application of the mRS in clinical trials of acute ischemic stroke treatments.
Construct Validity: Relationship to Stroke Severity
Construct validity of the mRS has been affirmed by multiple studies in which it has been consistently observed that the location, type and extent of stroke injury are closely related to short and longer-term disability (Table 3; detail in supplemental Table I, available online at http://stroke.ahajournals.org). Numerous investigations have reported an increased risk of poor outcome (defined as mRS >2 or >3) from discharge to 6 months for more severe types of stroke.1928 For example, a study of 198 younger ischemic stroke patients showed that total anterior circulation infarction was an independent predictor of mRS grade
2 or death at 3 months (P=0.011).22 Similar results have been reported for older stroke populations.27,28
Studies in small patient series have consistently shown significant relationships between lesion volume (measured by diffusion-weighted and other imaging methods) and mRS grades (Table 3; detail in supplemental Table I), with larger lesions predicting more severe disability.20,2934 As would be reasonably expected, improved brain perfusion and recanalization after thrombolytic therapy are also associated with improved mRS disability outcomes.21,33,35,36 For example, in a study of 177 acute ischemic stroke patients, recanalization within 5 hours postrecombinant tissue plasminogen activator treatment (in addition to National Institutes of Health Stroke Scale [NIHSS] baseline scores and other factors) independently predicted mRS grade
2 at 3 months poststroke (odds ratio=4.11, 95% CI=2.42 to 6.95; P<0.001).21
Multivariate regression analyses have demonstrated that acute impairment score (measured with the NIHSS,2022,37 Canadian Neurological Scale,26,38 Mathew scale,31 Los Angeles Motor Scale,39 or European Stroke Scale40) independently predict mRS grade at 2 months to 1 year poststroke (detail in supplemental Table I). For example, Demchuk and coworkers observed that patients with the mildest strokes (NIHSS score 1 to 5) compared with those with more severe strokes (NIHSS scores 11 to 15, 16 to 20, >20) had improved chances of achieving a favorable outcome defined by mRS grade 0 to 1 (95% CI=0.02 to 0.16, P<0.001; 95% CI=0.13 to 0.56, P<0.001; 95% CI=0.20 to 0.79, P=0.008, respectively).41 Transitions in mRS grades have also been shown to correspond to transitions in NIHSS scores during stroke recovery.11 Consistent with these observations, moderate to strong correlations (Pearson r=0.60 to 0.86) between acute impairment and mRS grades at discharge or follow-up have also been reported.38,40,42,43 Specific impairments that appear to contribute significantly to the more severe mRS grades include those involving alertness, orientation, leg motor function, following commands, and arm and hand function (detail in supplemental Table I).23,44,45
Convergent Validity: Relationship to Other Disability Scales
Convergent validity of the mRS has been demonstrated by comparisons with other disability scales used to evaluate stroke patients, including the American Heart Associations Stroke Outcomes Classification (AHA.SOC), the BI, the motor component of the Functional Independence Measure (m-FIM), the Short Form-36 (SF-36), and the Stroke Impact Scale (SIS; Table 4; detail in supplemental Table II, available online at http://stroke.ahajournals.org).8,11,43,4648 For example, using stroke registry data, Kwon and coworkers quantified the frequency distribution of BI scores relative to mRS grades and showed that the highest BI scores (95 to 100, indicating excellent to complete recovery) correspond to mRS grades 0, 1 and 2.46
The particular relationship between the BI and the mRS has been explored in detailed investigations,7,8,46,48 reflecting the common use of these scales as end points in acute stroke treatment RCTs. Post hoc and quantitative translations between mRS grades and BI scores have been derived to facilitate comparisons among trial results.7,48 Whereas the correlation between trial end points of both scales is strong (r=0.89, P<0.001),43 their different structures, domains and scoring methods provide distinctive information. As described previously, the BI measures dependence in 10 BADLs, whereas the mRS captures higher functioning in addition to aspects of self-care. Eight of the ten BI domains reflect voluntary motor functions (see footnote
). However, poststroke disability can also affect speech, language or cognitive function.49 For example, a patient with substantial communication problems may still score
90 on the BI. This "ceiling effect" is a major disadvantage of the BI relative to a global disability instrument.9,45,46,4951 Data from a large prospective cohort study of stroke patients demonstrated the limitations of the BI in mild stroke patients.45 The mRS was also reported to be more sensitive for distinguishing between mild and moderate disability, which suggests it may also be more sensitive to acute stroke treatment effects.45
Clinical Sensitivity
The clinical sensitivity or responsiveness of an instrument refers to its ability to detect a clinically important change.52 Limited information is available regarding the sensitivity of the mRS to changes in disability levels after a stroke. In a rehabilitation setting the sensitivity of 2 global disability measures, the mRS and the International Stroke Trial Measure (ISTM),53 and 2 ADL measures, the BI and FIM,54 were tested and compared in a nonrandom sample of 95 moderately disabled stroke patients.52 A change of one mRS grade was considered to be clinically significant based on the range of severity covered by the scale grades. Although the mRS was shown to be more sensitive than the ISTM (P<0.001), it was less sensitive than either the BI (P<0.002) or the FIM (P<0.005), with the latter being the most sensitive of the 4 instruments under the conditions of the study. On this basis, the authors recommended the use of ADL scales for stroke intervention trials. However, other analyses (see below) based on treatment effects anticipated in the acute stroke setting suggest that those effects may be better detected using the mRS.
Limitations
A number of limitations apply to the mRS when used to measure disability outcome after stroke. A substantial literature documents the negative effect of patient comorbidities (including cardiovascular disease, diabetes, and arthritis),5558 surgery,59 and socioeconomic factors60 on physical functioning, cognitive abilities,58 and overall health status, factors that may have a direct impact on the mRS.59 This is particularly important because comorbidities are common in stroke patients and the incidence of stroke in socioeconomically disadvantaged populations is especially high.61 It is essential for the clinician to take these various attributes into account to avoid misapplication and misinterpretation of the mRS.
End Point in Clinical Trials
The mRS has been used often as an end point in RCTs of acute ischemic stroke treatments based on its straightforward application, acceptable inter-rater reliability, and ability to discriminate levels of stroke disability.45,46 Studies have found that the sample size requirements of trials using mRS-based end points are smaller than BI-based end points without the loss of statistical power.50,62 For example, the sample required for a neuroprotectant RCT using a mRS end point (dichotomized at grade
1) was estimated to be 38% of that required for a BI end point (dichotomized at
60).50
Optimizing mRS end points for acute stroke treatment RCTs involves careful definition and appropriate statistical analyses. A "favorable" outcome defined as mRS grade
1 or
2 was estimated to be more powerful than dichotomization at higher grades.3,63,64 The importance of the cut-point for dichotomization was illustrated in a post hoc analysis of the ECASS II trial of alteplase. This study found that expanding the definition of "favorable" outcome from mRS grade
1 to grade
2 changed a statistically insignificant result to a significant one.3,64 Concerns over dichotomized end points center on the risk of failure to detect the impact of treatment. In a prospective study of 459 stroke patients, 116 subjects had transitioned from a baseline mRS score of 5 to a 3-month score of 4 or 3; or, from a baseline score of 4 to a 3-month score of 3.11 If those observations apply to RCTs, the reported shifts in mRS grades of more severe stroke patients toward reduced disability may not be captured by an end point defined as mRS
2,11 even though all mRS grade transitions are considered to be clinically meaningful.65
Transition across the entire mRS grade spectrum has been proposed as a more comprehensive measure of impact for acute stroke interventions.11,66 This type of analysis uses the entire data set and has the advantage of reflecting simultaneously the risk and benefit of an intervention compared with an analysis based on a dichotomized end point. The SAINT I trial of the neuroprotectant NXY-059 for acute ischemic stroke exemplifies this approach.65 In this trial, the primary end point was prespecified as the mRS grade at 90 days (or last rating) with the analysis based on the overall difference in grade distribution of the 2 treatment groups.
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Summary and Conclusions
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A large and diverse literature supports the view that the mRS
is a valid and clinically relevant instrument for assessing
recovery from stroke and is a valuable end point for RCTs of
acute ischemic stroke treatments. The scale consists of well-defined
and easily understood grades that describe the range of global
disability. When properly administered, the mRS exhibits a strong
relationship with clinical measurements of stroke severity in
addition to other disability and outcomes end points. However,
clinicians should be aware that mRS grading may be affected
by a variety of factors, including patient comorbidities and
socioeconomic status. Use of the mRS in RCTs may benefit from
a carefully defined end point as well as from a form of statistical
analysis that is most likely to accurately reflect the effect
of treatment.
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Acknowledgments
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The authors gratefully acknowledge the financial sponsorship
of AstraZeneca LP. We greatly appreciate the contributions of
Chris Pashos, PhD for his review and comments and of Yoko Komatsuzaki,
MPH, Er Chen, MPP, Yu-Chen Yeh, MS and Cassie Cai, MS, MS for
their administrative and editorial assistance.
Disclosures
None.
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Footnotes
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*The mRS was not developed for the acute assessment of stroke.
For example, the scale would have limited value if it were used
in the acute setting as illustrated by assigning a patient with
a mild stroke mRS grade 4 or 5 on the basis of the need for
nursing care and supervision.

The Barthel Index ADL items are: feeding, bathing, grooming, dressing, bowels, bladder, toilet use, transfers, mobility, stairs.13 
Strength of agreement for the
statistic has been categorized as follows: <0=poor; 00.20=slight; 0.210.40=fair; 0.410.60=moderate; 0.610.80=substantial; 0.811.00=almost perfect.67 
Received August 29, 2006;
revision received October 5, 2006;
accepted October 6, 2006.
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