THE WORLD HEALTH ORGANIZATION defines mobility

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1 9 Validity and Reliability Comparison of 4 Mobility Measures in Patients Presenting With Neurologic Impairment Philippe Rossier, MD, Derick T. Wade, MA, MD, FRCP ABSTRACT. Rossier P, Wade DT. Validity and reliability comparison of 4 mobility measures in patients presenting with neurologic impairment. Arch Phys Med Rehabil 2001;82: Objective: To establish the reliability and validity of 4 mobility measures in neurologically impaired adults undergoing rehabilitation. Design: Repeated assessment of same patients. Setting: Two specialized neurologic centers in England. Patients: Forty-six patients with neurologic disabilities selected from inpatient and outpatient rehabilitation centers who were able to stand and walk at least 10 meters, with some aid if needed. Interventions: Patients were assessed twice, at an interval of 7 days, by the same person at the same location. Validity and reliability of each measure were compared by means of scatterplots, Bland-Altman method, and correlation coefficients. Validity was also established by comparing groups of patients expected to differ in mobility. Main Outcome Measures: The Rivermead Mobility Index (RMI) standard version and a version with 4 levels of answer, the 10-meter timed walk, and the 2-minute walk test. Results: The measures showed significant intercorrelation, suggesting that all were valid mobility measures. Each was reasonably reliable, with no evidence of systematic bias. The revised RMI was less sensitive to differences. The distance covered in the 2-minute walk test was significantly decreased for patients using aids (p.0005) and those with impaired leg sensation (p.02). Conclusions: All 4 measures tested (2 RMI versions, 1-meter timed walk, 2-minute walk test) showed similar validity and reliability, and the 4-level RMI version failed to show an increased ability to detect differences. All measures showed more disability in patients using aids and those with sensory impairment. Key Words: Gait disorders, neurologic; Rehabilitation; Rivermead Mobility Index; Walking by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation THE WORLD HEALTH ORGANIZATION defines mobility as the individual s ability to move about effectively in his surroundings. 1 Recently, van Bennekom et al 2 gave a more general definition: Mobility is the process of moving oneself, From the Rivermead Rehabilitation Centre, Oxford, UK. Accepted in revised form March 17, Supported in part by the SICPA Foundation, Lausanne-Prilly, Switzerland. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the author(s) is/are associated. Reprint requests to Derick T. Wade, Rivermead Rehabilitation Centre, Abingdon Rd, Oxford OX1 4XD, UK, derick.wade@dial.pipex.com /01/ $35.00/0 doi: /apmr and of changing and maintaining postures. To most patients, loss of mobility is perhaps the single activity of daily living on which they place the most value. 3 Measuring mobility can assist the clinician in diagnosis, choice of the most appropriate therapy, and outcome measurement. 4-6 Many instruments have been developed to assess mobility, 7-12 but few studies compared measures or investigated reliability. In addition, there is a general assumption that having more measuring tiers within a multi-item scale increases its sensitivity. For example, the FIM TM instrument 13 and the modified Barthel index 14 are based on this assumption. Some studies challenge this assumption. 15,16 This study investigates the reliability and validity of some common clinical assessments: the Rivermead Mobility Index 7,17 (RMI) in both its standard form and a new 4-level version, the 10-meter timed walk, 8 and the 2-minute walk test, 9 which has not been used much with neurologically impaired patients. METHODS Subjects were inpatients or outpatients at 2 specialist neurologic rehabilitation centers (Rivermead Rehabilitation Centre, Ritchie Russell House). All presented with severe impairment caused by a neurologic disease. To be included on the study, patients had to provide informed consent, be in a clinically stable state that was not likely to change over 1 week, and be able to walk at least 10 meters with or without aids. Every patient was assessed using the RMI 7,17 questionnaire, scoring the answers in 2 ways: using the standard method (yes 1, no 0) and a new version with 4 possible answers (able to do it alone 3 points, with some aid 2 points, with someone 1 point, unable to do it 0). Each patient was asked to walk on a 10-meter walkway for 2 minutes at their own speed, using the aid of their choice if needed. We measured the time taken to walk the first 10 meters 8 and the number of meters walked during 2 minutes. 9 One week later, the same tests were repeated at the same location, with the same aids if needed and the same observer. On each occasion, a brief, clinical neurologic examination also was performed, specifically noting the presence or absence of impaired sensory function of the legs. The Bland-Altman 18 method was used to assess agreement between the first and second test for the 4 measures. In this method, the average scores of the first and second occasions are plotted against the difference between scores. We used the t test and Mann-Whitney U test to detect a statistically significant difference between occasions and between different subgroups using the same measure. In addition, we plotted scattergrams to compare results between occasions and between different measures, calculating Spearman s or Pearson s correlation coefficients, as appropriate. To investigate the construct validity of the 2 RMI versions, we divided the patients into 2 groups, using the median distance walked in 2 minutes (57m) to characterize a fast and slow group. We calculated the mean score with standard deviation (SD) for the 2 RMI versions in each group and the t test for

2 10 VALIDITY AND RELIABILITY OF 4 MOBILITY MEASURES, Rossier n 46. Table 1: Neurologic Diagnoses Diagnosis Stroke 21 Head injury 8 Tumor 3 Myelopathy 3 Huntington s disease 3 Postanoxic encephalopathy 2 Encephalitis 1 Epilepsy/ill-defined brain damage 1 Polyneuropathy 1 Myotonic dystrophy 1 Cervical arteriovenous malformation 1 Multiple sclerosis 1 comparing which version best detected the difference between the fast and slow groups. To perform a complementary validity investigation of all tests, we divided patients into 2 groups according to their use of additional equipment and into 2 other groups according to the presence or absence of leg sensory impairment. For each n group, we calculated the mean score with SD for the 4 different measures of mobility. We hypothesized that patients using equipment would have lower levels of mobility compared with those not using equipment, and that patients with sensory impairment would have lower levels of mobility compared with those without sensory impairment. RESULTS Forty-six patients were assessed over 2 months. The mean time SD between onset of neurologic disease and assessment was 6 7 years; 36 (78%) patients had a stable neurologic state, and the remainder had a very slowly progressive disease. The mean age was years, 28 (61%) were men, and 23 (50%) used an aid when walking (rollator, Arjo rollator, stick, splint). Sixteen (35%) patients had some impaired sensation in the legs, alone or with other impairments. The main neurologic diagnoses are listed in table 1. For all patients, the neurologic examination did not show a difference between examinations 1 and 2, and all patients were considered neurologically stable. The reliability for the 4 measures is shown in figures 1A D and 2A D. Using the Bland-Altman method, the nearer the points are to the zero line, the greater the test s reliability. There was no significant difference (95% confidence interval) in score between the first and second occasions in any of the Fig 1. Scatterplots of results comparing time 1 versus time 2: (A) RMI 0 to 15 score, (B) RMI 0 to 45 score, (C) 10-meter time walked (s), and (D) distance walked (m) in 2 minutes.

3 VALIDITY AND RELIABILITY OF 4 MOBILITY MEASURES, Rossier 11 Fig 2. Bland-Altman method to plot difference of scores against mean score of times 1 and 2: (A) RMI 0 to 15 score, (B) RMI 0 to 45 score, (C) 10-meter time walked (s), and (D) distance walked (m) in 2 minutes. Difference time 1 time 2. tests (table 2). The intercorrelation coefficients between tests 1 and 2 for the same test and between different tests performed at the same time were all high (table 3). A few outliers appear on the scatterplots; eg, on the 10-meter timed walk, 1 patient took 150 and 259 seconds, with a difference of 109 seconds between tests 1 and 2. The neurologic examination before the 10-meter walk was the same for assessments 1 and 2, although patient said he was particularly tired on the day of test 2. For the same patient, the standard RMI scores were the same for tests 1 and 2 (3 points), whereas the revised RMI scores showed an improvement for test 2 (19 vs 23 points). As noted, we divided the patients into 2 groups according to their performance at the 2-minute walk. The mean RMI 4-level score for the fast group was 40.9 ( 3.2), and for the slow group, 31.2 ( 7.7); this difference was not significant (t test, p.11). In comparison, the standard RMI scores showed mean values of 12.9 ( 2) and 8 ( 3.3), respectively; this difference was statistically significant (p.02). A similar analysis was performed using the median 10-meter time to group patients when the statistical significance of the difference still favored the original scoring method (p.05, p.01). This suggests that the standard scoring method is more able to detect the expected differences. Table 4 lists the results of the 4 measures of mobility for the patients walking with or without aids and for the patients presenting with or without a sensory impairment in the legs. These results confirm the hypothesis that mobility level is less in patients using an aid and those presenting with a leg sensory impairment. The 4 measures also are able to detect the expected difference. The data for the 2-minute walking distance (table 5) showed that all subjects (except 1) who were not able to walk more than 40 meters in 2 minutes used some equipment. With an appropriate device, the single exception should be able to improve extensively his performance in 2 minutes. People walking more than 80 meters did not need aids. Between these 2 values, approximately half the patients used aids. DISCUSSION The present study suggests that simple measures of mobility are reliable when performed by a single observer and can detect predicted differences in a range of patients with neurologic disorders. However, the study also suggests that increasing the

4 12 VALIDITY AND RELIABILITY OF 4 MOBILITY MEASURES, Rossier Table 2: Observed Percentile Interval Scores for Each Measure on Each Test Occasion and Difference in Scores Score Item Minimum 5% 50% 95% Maximum Mean* Test 1 RMI 0 to (3.7) RMI 0 to (7.6) 10-meter timed walk (s) (34.3) 2-min walk (m) (34.2) Test 2 RMI 0 to (3.9) RMI 0 to (8) 10-meter timed walk (s) (44.7) 2-min walk (m) (35.6) Difference RMI0to (1.12) RMI0to (2.29) 10-meter timed walk (s) (17.9) 2-min walk (m) (9.07) Difference equals test 1 test 2. * Values expressed as mean (SD). possible score range for a single criterion in a questionnaire does not necessarily improve sensitivity. This study did not examine interrater reliability or homogenous groups of patients. In addition, all patients were able to walk, limiting generalizability to similar patients. This study included patients with a wide range of diagnoses and impairments; the common factor was reduced mobility. This is both a weakness and a strength of the study. In clinical practice, use of similar measures for all patients with similar problems improves outcomes, and this study suggests using these measures to assess mobility in most patients who walk. It is possible, but unlikely, that the findings would be different in patients with specific diseases. If this measure is to be used in research examining a specific group, it might be wise to establish the limits of its reliability with those patients. Table 3: Intercorrelation Coefficients for Test Occasions RMI 0to15 RMI 0to45 10-M Timed Walk 2-Min Distance RMI0to RMI0to meter timed walk min distance.97 All data from first assessment, except when test 1 with test 2 are from same test (boldface). The study investigated validity in some circumstances but did not test sensitivity to change over time. The main finding is that all measures could detect the expected difference between fast and slow walkers, patients with or without sensory impairment, and patients who did or did not use aids. One important observation is that increasing the apparent sensitivity of a measure by increasing the gradation of possible responses does not necessarily increase sensitivity. The relative reliability of the 4-level and 2-level RMI scales was similar; the 4-level scale was proportionately more reliable. Nonetheless, the standard scale was able to detect differences better. Few other similar studies confirm this conclusion, but similar observations have been made for the Barthel index. 15 The measures show relatively close intercorrelations. This could be construed as evidence of validity; however, the scales measure different aspects of mobility. The RMI covers a larger range, starting with basic bed mobility; the 10-meter time measures short-duration speed; and the 2-minute walking test assesses endurance (which may be affected by such factors as arthritic pain and cardiovascular fitness). The 2-minute walking test may be the most relevant to patients. Other aspects of mobility can be assessed by using other measures. 19,20 CONCLUSION The RMI scored using the standard system (0 15), timed walking over 10 meters, and distance walked in 2 minutes are Table 4: Differences in Scores for Each Test, Comparing Use of Aid and Sensory Impairment Measures Aid (n 23) No Aid (n 23) p Sensory Loss (n 16) No Sensory Loss (n 30) p RMI0to15 Mean (SD) 7.9 (3.2) 12.8 (2.3) (3.6) 11.1 (3.6).035 Median RMI0to45 Mean (SD) 31.8 (7.5) 40 (5) (7.5) 37.6 (7.1).017 Median meter timed walk (s) 43.4 (46.9) 13.5 (5.4) (52.2) 23.8 (28.6) min walk (m) 37.9 (20.9) 83.9 (30.1) (27.6) 68.3 (36.1).022

5 VALIDITY AND RELIABILITY OF 4 MOBILITY MEASURES, Rossier 13 Table 5: Distances Walked (m) in 2 Minutes by Patients With and Without Walking Aids Equipment (n 23) No Equipment (n 23) Time (s) Rank order Rank order Time (s) p reliable and valid mobility measures in patients with neurologic disease. The measurements can also detect differences between patient groups. All measures are simple and should be used widely in clinical practice and medical research. Acknowledgments: The authors thank the patients who participated in this study and Professor A. So and the staff for their help. References 1. World Health Organization. International classification of impairment, disabilities, and handicaps; a manual of classification relating to the consequences of disease. Geneva: World Health Organization; van Bennekom CAM, Jelles FJ, Lankhorst GJ. Rehabilitation activities profile: the ICIDH as a framework for a problemoriented assessment method in rehabilitation medicine. Disabil Rehabil 1995;17: Chiou IL, Burnett CN. Values of activities of daily living: a survey of stroke and their home therapists. Arch Phys Med Rehabil 1985;65: Wade DT. Measurement in neurological rehabilitation. Oxford: Oxford Univ Pr; Geurts ACH, Mulder TH, Rijken RAJ, Nienhuis B. From the analysis of movements to the analysis of skills: bridging the gap between laboratory and clinic. J Rehabil Sci 1991;4: Lincoln NB. Research methodology. Clin Rehabil 1990;4: Collen FM, Wade DT, Robb GF, Bradshaw CM. The Rivermead Mobility Index: a further development of the Rivermead Motor Assessment. Int Disabil Stud 1991;13: Collen FM, Wade DT, Bradshaw CM. Mobility after stroke: reliability of measures of impairment and disability. Int Disabil Stud 1991;12: Butland RJA, Pang J, Gross ER, Woodcock AA, Geddes DM. Two, six and twelve minute walking tests in respiratory disease. Br Med J 1982;284: Goldfarb BJ, Simon SR. Gait patterns in patients with amyotrophic lateral sclerosis. Arch Phys Med Rehabil 1984;65: Holden MK, Gill KM, Magliozzi MR, Nathan J, Piehl-Baker L. Clinical gait assessment in the neurologically impaired: reliability and meaningfulness. Phys Ther 1984;64: May D, Nayan USL, Isaacs B. The life-space diary: a measure of mobility in old people at home. Int Rehabil Med 1985;7: Hamilton BB, Laughlin JA, Fiedler RC, Granger CV. Inter-rater reliability of the 7-level Functional Independence Measure (FIM). Scand J Rehabil Med 1994;26: Shah S, Vanclay F, Cooper B. Improving the sensitivity of the Barthel index for stroke rehabilitation. J Clin Epidemiol 1989;42: Hocking C, Williams M, Broad J, Baskett J. Sensitivity of the Shah, Vanclay and Cooper s modified Barthel index. Clin Rehabil 1999;13: van der Putten JJMF, Hobart JC, Freeman JA, Thompson AJ. Measuring change in disability after inpatient rehabilitation: comparison of the responsiveness of the Barthel index and the Functional Independence Measure. J Neurol Neurosurg Psychiatry 1999;66: Forlander DA, Bohannon RW. Rivermead Mobility Index: a brief review of research to date. Clin Rehabil 1999;13: Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: Wolfson L, Whipple R, Amerman P, Tobin JN. Gait assessment in the elderly: a gait abnormality rating scale and its relation to falls. J Gerontol 1990;45:M Lord SE, Halligan PW, Wade DT. Visual gait analysis: the development of a clinical assessment and scale. Clin Rehabil 1998; 12:

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