AFTER STROKE, MANY PEOPLE have problems with. Reliability and Validity of the Dynamic Gait Index in Persons With Chronic Stroke ORIGINAL ARTICLE

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1 1410 ORIGINAL ARTICLE Reliability and Validity of the Dynamic Gait Index in Persons With Chronic Stroke Johanna Jonsdottir, ScD, Davide Cattaneo, PT ABSTRACT. Jonsdottir J, Cattaneo D. Reliability and validity of the Dynamic Gait Index in persons with chronic stroke. Arch Phys Med Rehabil 2007;88: Objective: To establish the test-retest and interrater reliability as well as the concurrent construct validity of the Dynamic Gait Index (DGI) as a measure for dynamic balance in people with chronic stroke. Design: Cohort study. Setting: Day hospital and ambulatory care at a rehabilitation center. Participants: A consecutive sample of 25 participants, at least 3 months poststroke and able to walk at least 10m with or without a walking aid, participated in the study. Two independent raters rated performances on the DGI. Interventions: Not applicable. Main Outcome Measures: The DGI was administered in 2 testing sessions 3 days apart. In the second session, the participants were rated by 2 raters. Intraclass correlation coefficients (ICCs), model 2,1, and the Bland and Altman method were used to analyze total scores and item scores. Concurrent construct validity was tested by correlating results to the Berg Balance Scale, the timed walking test, the Timed Up & Go test, and the Activities-specific Balance Confidence Scale. Results: ICCs for test-retest and interrater reliability of total scores were good (.96,.96, respectively) whereas reliability for single item scores was moderate to good (range,.55.93). The hypotheses for concurrent construct validity were confirmed with all measures (range,.68.83). Conclusions: The DGI showed high reliability and showed evidence of concurrent validity with other balance and mobility scales. It is a useful clinical tool for evaluating dynamic balance in ambulatory people with chronic stroke. Key Words: Balance; Gait; Rehabilitation; Reliability and validity; Stroke by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation AFTER STROKE, MANY PEOPLE have problems with balance during movement and gait activities. These problems often persist into the postacute stage and can limit general function and participation in daily life. In consequence, an important emphasis in rehabilitation for people with chronic stroke is the development of interventions for improving balance From LaRiCE: Clinical Laboratory on Posture and Gait, Don Gnocchi Foundation I.R.C.C.S., Milan, Italy. 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 author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Johanna Jonsdottir, ScD, Servizio riabilitazione neurologica adulti (Int. 282), Don Gnocchi Foundation I.R.C.C.S., Via Capecelatro 66, Milan, Italy, jjonsdottir@dongnocchi.it /07/ $32.00/0 doi: /j.apmr and mobility function. Reliable and accurate measures of balance are fundamental for planning treatment and measuring outcome. Measuring dynamic balance is an especially important issue in people with stroke because most falls occur during movement. 1,2 Although balance performance in people with stroke has been well documented in dynamic standing and during quiet standing with altered sensory inputs, 3-6 there is a scarcity of measures available to evaluate their dynamic balance during gait activities. The Dynamic Gait Index (DGI) was developed by Shumway-Cook and Woollacott 7 to evaluate functional stability during gait activities in older people and to evaluate their risk of falling. The DGI includes items such as walking while changing speed and turning the head, gait with pivot turn, walking over and around obstacles, and stair climbing. People with stroke tend to have problems with sensory and neuromotor organization and with controlling momentum during movement A scale such as the DGI might be useful in capturing problems that cannot be detected with more static balance measures. Further, the use of the DGI for the stroke population may allow a simple evaluation of falls risk in that population. The DGI has been found to be reliable and valid in other populations including older adults, people with multiple sclerosis (MS), and people with vestibular dysfunction The aim of this study was to examine the interrater and test-retest reliability, as well as the concurrent construct validity of the DGI for people with stroke. Reliability was assessed by calculating the intraclass correlation coefficient, model 2,1 (ICC 2,1 ). A priori, based on the literature, we had decided that ICCs of 0.80 to 1.00 indicated good reliability,.60 to.79 was acceptable,.40 to.59 was moderate, and less than.40 was weak. 17 To examine concurrent construct validity, we selected other measures of balance and functions that would be affected by dynamic balance as comparators. We hypothesized that the DGI would have a moderate positive correlation with the Berg Balance Scale (BBS) 18 and the Activities-specific Balance Confidence (ABC) Scale, 19 and a moderate negative correlation with the timed walking test 20 and the Timed Up & Go (TUG) test. 21 METHODS Participants A consecutive sample of 25 people with stroke participated in the study. The reliability testing of the DGI was done as a pilot study for a larger project intended to study the general characteristics of standing and gait equilibrium in people with chronic stroke. Sample size was based on an examination of similar studies in the literature. The participants were all receiving rehabilitation services at the Don Gnocchi Foundation in Milan as either day hospital patients (n 3) or outpatients (n 22) for the period between February and September The inclusion criteria were that participants had a first-ever stroke, were at least 3 months poststroke, were capable of walking 10m with or without an aid, and were capable of understanding and following instructions. Each participant signed an informed consent form before participating in the

2 RELIABILITY OF DYNAMIC GAIT INDEX FOR STROKE, Jonsdottir 1411 Descriptive Statistics Table 1: Test Scores on All Tests Administered Barthel Index DGI 1* DGI 2 DGI 3 BBS ABC TWT (m/s) TUG (s) Mean SD Range Abbreviation: TWT, timed walking test. *Mean test scores first assessment by rater 1. Mean test scores second assessment by rater 1. Mean test scores second assessment by rater 2. study. Of the 25, 18 were men and 7 were women; mean age of the sample standard deviation (SD) was years (range, y) and mean time from onset was years (range, y). Nineteen of the 25 participants used walking aids outside of the home, but only 6 of those 19 used a walking aid at home. Three participants used a tripod as a walking aid and the remaining 16 (of 19) used a cane. Nine participants had left-hemisphere stroke and 14 had right-hemisphere stroke. All participants were administered the Barthel Index 22 of functional independence (table 1). Their ability to understand and follow instructions was verified with their clinicians and treating therapists. Procedures Two physical therapists (rater 1, JJ; rater 2, DC) rated the performance. Both raters had more than 10 years of experience in evaluating patients with neurologic problems and had previously used the DGI for other patient populations. To examine test-retest reliability the DGI was administered to each participant by rater 1 in 2 testing sessions 3 days apart. To allow evaluation of interrater reliability the DGI was rated simultaneously by rater 2 in the latter testing session. The 2 raters were not allowed to consult each other during the test and had no access to previous test results. The participants who walked in their home without a cane did so as well during the DGI testing session, and the 6 patients who felt the need to use the tripod or cane inside their home did the test with their walking aids. The participants who used ankle-foot orthoses (n 7) used those during the testing session. All participants used their normal shoes. The DGI was always administered in the same space and participants were given the standard verbal instructions of the DGI. It was necessary to demonstrate item 5 (gait and pivot turn) to the participants while describing the task. The timed walk test, the TUG, and the BBS were administered and rated by rater 1 immediately after the first session to test concurrent validity of the DGI. The self-administered ABC was also collected at the first session. The whole testing protocol in the first session took 40 to 45 minutes. Participants were allowed to rest between the various tests if necessary. In the second session, only the DGI was performed. Measurement Scales Dynamic Gait Index. The DGI has 8 items: walking, walking while changing speed, walking while turning the head horizontally and vertically, walking with pivot turn, walking over and around obstacles, and stair climbing. The scoring of the DGI is based on a 4-point scale ranging from 0 to 3, with 0 indicating severe impairment and 3 indicating normal ability. The best performance total score is 24. A low composite DGI score thus indicates greater impairment in functional mobility. The DGI has been found to be reliable and valid for older people (.96). 13 Reliability for the DGI as an evaluation tool has also been verified and found to be high for people with vestibular dysfunction (.95) 14 and for people with MS (ICC.98). 15,16 In a recent Rasch analysis of items of the DGI, it was found to have sound psychometric properties and be clinically relevant for older people. 23 Further, the DGI has been shown to correlate moderately with self-reported fall history in older people 24 and in people with vestibular dysfunction. 25,26 Scores of or below 19 points on the DGI indicate a risk of falling in older people and in people with vestibular dysfunction. 25,27 In a population of subjects with MS, a score of less than 12 points discriminated between fallers and nonfallers. 28 Concurrent validity of the DGI has been investigated for the above groups comparing it with, among other tests, the BBS and the ABC. 18,19 Berg Balance Scale. The BBS was originally constructed to assess balance ability of older people and identify their risk for falling. 18 The BBS is a 14-task scale that requires subjects to maintain their balance in positions and tasks of increasing difficulty. Specific components of the BBS parallel some gait requirements such as unsupported leg stance and standing with 1 foot in front of the other. Other components address tasks such as rising to stand or standing unsupported. It has an ordinal scale of 0 to 4 points (best performance, 56). The BBS is well documented and has strong psychometric properties for older people, for people with MS, and people with stroke. 15,29 For subjects with stroke, the interrater and intrarater reliability were found to be.97 and.98, respectively. A score of 44 or less has been found to indicate a higher risk of falls. 29 ABC scale. The ABC is a 16-item self-report questionnaire that asks people to rate their balance confidence in performing everyday activities on a numeric rating scale (range, 0 100). 19 A score of zero represents no confidence and a score of 100 represents complete confidence in performing the activity. Botner et al 30 showed high test-retest reliability of the ABC (ICC.85) and a low to moderate linear correlation of the ABC with the BBS and gait speed (r.36, r.48, respectively) for people with stroke. A moderate correlation (r.58) has been found between the ABC total score and the DGI in people with vestibular dysfunction. 31 Timed walking test. For the timed walking test, the participant is timed while walking 10m at their comfortable speed. 20 The timed walking test has been found to have high test-retest reliability in people with stroke (ICC.87). 32 Gait speed reflects aspects of walking abilities and is commonly used to measure mobility in people with neurologic dysfunction. Slower walking speeds have been found to correlate with balance dysfunction in people with stroke. 20 Timed Up & Go test. The TUG is a simple functional test that requires a person to stand up, walk 3m, turn back, and sit down again while being timed. 21 The TUG has been found to have excellent test-retest reliability in people with stroke (ICC.95). 33 Time taken to complete the test has been shown to be correlated to levels of functional mobility and with scores on the BBS as well as with scores on the DGI for people with MS. 16 Scores of 13.5 seconds and above on the TUG indicate

3 1412 RELIABILITY OF DYNAMIC GAIT INDEX FOR STROKE, Jonsdottir Table 2: ICCs and Confidence Intervals of DGI Total and Item Scores, Test-Retest, and Interrater Conditions Item ICC Test-Retest 95% CI ICC Interrater 95% CI Total score Item 1. Gait level surface Item 2. Change in gait speed Item 3. Gait with horizontal head turns Item 4. Gait with vertical head turns Item 5. Gait and pivot turns Item 6. Step over obstacle Item 7. Step around obstacles Item 8. Steps Abbreviation: CI, confidence interval. an increased risk of falling in older adults and in people with vestibular dysfunction. 34 Statistical Analysis We used descriptive statistics to describe the characteristics of the sample. Test-retest and interrater reliability of total DGI scores and item scores were statistically evaluated using the ICC 2,1, 35 and the Bland and Altman method 36 in accordance with the recommendations of Rankin and Stokes. 37 The method of Bland and Altman was used for assessing agreement between sessions and between raters and for calculating the mean difference between measurements and the SD of the difference. The individual total scores of the first or second assessment and the individual total scores of rater 1 and rater 2 were plotted against the difference between scores. The Bland and Altman method allows a visual representation of the degree of agreement, and an identification of bias, outliers and any relationship between the variance in measures with the size of the mean. The nearer the points are to the zero line, the better the test s reliability. The standard error (SE) of measurement of the total score was calculated for both the test-retest and the interrater conditions to determine the consistency of scoring in absolute terms and to evaluate the minimal detectable change. Given a normal distribution and no change, 68% of the time an observed score will fall within 1 SE of measurement of a person s true score, and 95% of the time it should fall within 1.96 SE of measurement of the true score. 38 To examine concurrent validity of the DGI for this population, we calculated Spearman correlation coefficients to determine the correlation between the total DGI score and the time it took to complete the timed walking test and the TUG as well as the total scores on the BBS and the ABC. The criterion for statistical significance was P less than.05. RESULTS The participants mean scores on the DGI, the BBS, the ABC, the timed walking test, and the TUG are shown in table 1, with ranges on all tests indicating a sample whose level of disability during testing and during activities of daily living varied from mild to moderate. No floor or ceiling effect was noted for any of the evaluation scales. Participants walked at a mean velocity of.45m/s, with the slowest participant walking with a velocity of.16m/s and the fastest participant walking with a velocity of 1.28m/s. Test-Retest Reliability The results are presented in table 2. The ICC for total scores for test-retest reliability was found to be very high at.96 (95% confidence interval [CI],.90.98). Item ICC scores for testretest reliability varied from 0.56 to Item 5 (gait and pivot turns) was the least reliable (.56). Items 1 (gait), 3 (gait with horizontal head turns), and 4 (gait with vertical head turns) had acceptable reliability (.64.77), whereas item 2 (changes in gait speed), item 6 (step over obstacles), and item 8 (climbing steps) had good reliability ( ). The Bland and Altman method of plotting the difference of scores against total scores of each participant of the 2 testing times showed good reliability (fig 1A). For the total score, the mean difference between A Differences B Differences Bland-Altman Test-Retest DGI Individual Total Scores Bland-Altman Interrater DGI Individual Total Scores Fig 1. Bland and Altman plots. The mean of individual total scores on the DGI are plotted on the x axis. Differences plotted on the y axis are the (A) difference in scoring between sessions by the same rater for the test-retest condition and (B) differences between 2 raters for the interrater condition.

4 RELIABILITY OF DYNAMIC GAIT INDEX FOR STROKE, Jonsdottir 1413 scores of the 2 testing sessions was All participants were within 2 SDs of the mean. The SE of measurement for the test-retest condition was.97. Interrater Reliability The results are presented in table 2. The ICC for total scores for interrater reliability was.96 (95% CI,.83.98). The ICCs on item scores ranged from 0.55 to 1.00 with gait with horizontal head turns (item 3) having the lowest reliability. Item 4 had acceptable reliability (.67) whereas all other items had good reliability ( ). The Bland and Altman method showed good reliability between the raters (mean difference, ). The mean differences in interrater scoring are plotted against the mean scores of the 2 raters for the same participant in figure 1B. All participants were within 2 SDs of the mean. The SE of measurement for interrater reliability was.94. Concurrent Validity The relationship between the DGI and the other measures confirmed the hypotheses. The BBS and the ABC showed a moderate positive correlation with the DGI at r equal to.83 and r equal to.68, respectively. The timed walking test and the TUG had a moderate negative correlation at r equal to.73 and r equal to.77, respectively. DISCUSSION The aim of this study was to investigate the reliability and concurrent validity of the DGI scale for people with stroke. The reliability of the total score on the DGI was high for both the test-retest and the between rater condition. The SEs of measurement were low indicating the ability of the DGI to detect small changes. Our reliability results are mostly similar to those obtained for groups of older participants, people with vestibular disorders, and people with MS In the study of McConvey and Bennett 16 interrater reliability was tested by the simultaneous scoring of 11 physical therapists from video recordings of DGI performances of 10 subjects with MS. For intrarater reliability the same video recordings were evaluated 2 weeks later. They found interrater reliability to be very high, but intrarater reliability was slightly lower than found in our study. In the study by Wrisley et al, 14 methods were more similar to those used in the present study, in that 2 experienced physical therapists simultaneously evaluated a live performance. They evaluated only interrater reliability and found that it was high between total scores, whereas for item scores was only moderate. Shumway-Cook et al, 13 using reliability procedures similar to those of Wrisley, found excellent interrater and test-retest reliability of the DGI for older adults when using total scores. Item reliability was found to be acceptable to excellent for all items. It was most difficult to agree on items 3, 4, and 5, which required the most subjective scoring. For item 5 (pivot turns) and for item 7 (step around obstacles), the reliability for the test-retest condition was lower than that of the interrater condition. The scores tended to be lower in the first rating session on these 2 items. It may be that there was a learning effect between sessions or that on hearing the instructions for the second time the subjects understood better what to do and therefore were more efficient at performing the activities. On item 8 (stair climbing), there was total agreement in both test-retest and the interrater condition indicating that instructions for item 8 were specific enough to leave little doubt about scoring. In general it was difficult to score items where qualitative changes in gait had to be agreed on, such as minimal gait deviations, significant gait deviations, or minimal changes in velocity. Item reliability of the DGI might be improved by providing more precise standardized instructions on administration of the test and more objective grading criteria for the items. Wrisley et al 39 have recently published a modified version of the DGI in which they attempted to provide more objective criteria for the rating of performance. Until now that version has been used only for people with vestibular disorders. Our ICCs for the item analysis tended to be higher than those of Wrisley, 14 who found low to good reliability of the DGI on several items. The lower reliability in their study on some items may be due to different statistical procedures as well as to differences in the population under study. Wrisley and colleagues did their reliability study on people who had vestibular disorders and no other specific physical impairments, and therefore their population showed only moderate to mild gait deviations. They used coefficient values for the item analyses, which may have been influenced by the low variability of their subjects who were skewed toward the higher end of the scale. In the present study, no participant scored the full possible score and patients performance ranged from 6 points to 21 of 24 possible. This variability of the sample may have increased our ICC values. On the other hand our results for the DGI item reliability differ more from those of McConvey and Bennett, 16 who found reliability to be very high for all items. Differences again may be due to reliability testing procedures. The moderate correlations between the DGI and the timed walking test, TUG, BBS, and the ABC support the concurrent construct validity of the DGI for evaluating elements of balance function in ambulatory people with stroke. The ABC showed the lowest correlation at.68, whereas the BBS, a clinical scale that evaluates static and dynamic equilibrium during activities in standing, was the highest at.83. All the scales above provide valuable information about people s functional balance activities. The ABC deals with people s selfperception of balance during daily activities, which can often be different from actual measures on clinical scales, whereas the BBS provides information about balance in sitting and standing activities. The TUG and timed walking test provide no direct information on balance per se, however, it is generally agreed that gait velocity provides a measure of functional gait and thus indirect information on balance during gait. In this study the correlation between the DGI and the BBS was slightly higher than that found for people with vestibular dysfunction (r.71) and people with MS (r.78). 15,40 The nonperfect correlation, however, indicates that the DGI may tap into other more dynamic aspects of balance function making it a valuable addition to clinical balance scales for people with stroke. Legters et al 31 found a moderate correlation of.58 between the ABC total score and the DGI in people with vestibular dysfunction. Our correlation values were slightly higher at.68 but the difference may be due to population differences. There is increased interest in balance rehabilitation for people with stroke. People with stroke have an increased risk of falling and often an increased fear of falling and both may contribute to decreased participation in daily living activities in the community. In fact, people with stroke often live a very sedentary life and seldom go outside except accompanied by family members. The DGI is potentially a tool that could help identify those at risk of falling. First, however, the sensitivity and specificity of the DGI in identifying fallers remain to be ascertained in people with stroke. Having a reliable measurement of balance function during gait activities may help in designing rehabilitation protocols aimed at improving dynamic function in activities of daily living. To evaluate these proto-

5 1414 RELIABILITY OF DYNAMIC GAIT INDEX FOR STROKE, Jonsdottir cols, the test s responsiveness to change needs to be determined. Study Limitations The DGI assumes that people are ambulatory, because the assessment is performed during over-ground walking; therefore it can only be applied to a population with stroke who are able to walk unassisted (but with an assistive device, if necessary) over ground. In the present study all the people were ambulatory, although many used a cane or tripod in daily activities. They were all very slow to moderately slow walkers in comparison to a healthy population. The results of the present study of the reliability of the DGI are generalizable only to a similar population. Although most of our subjects performed the DGI without an assistive device those who relied on an assistive device in their home (6 participants) performed the test with that device. The DGI for those participants becomes a 3-point scale, because it is impossible to score 4 points using an assistive device, and this may have increased the reliability of the measure. In the present study both raters were experienced neurologic physical therapists and because the DGI requires much subjective judgment on some items it might be less reliable with less experienced physical therapists or other health professionals. CONCLUSIONS We found the DGI (total score) to be a highly reliable clinical tool for evaluating dynamic balance in people with stroke. It also showed good concurrent construct validity. Further study of the scale s responsiveness and ability to predict falls is indicated. References 1. Shumway-Cook A, Baldwin M, Polissar N, Gruber W. Predicting the probability for falls in community-dwelling older adults. Phys Ther 1997;77: Harris J, Eng J, Marigold D, Tokuno CD, Louis CL. Relationship of balance and mobility to fall incidence in people with chronic stroke. 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