Get Up and Go Test in Patients With Knee Osteoarthritis

Transcription

1 284 Get Up and Go Test in Patients With Knee Osteoarthritis Sara R. Piva, MS, PT, OCS, FAAOMPT, G. Kelley Fitzgerald, PhD, PT, OCS, James J. Irrgang, PhD, PT, ATC, Fawzi Bouzubar, MS, PT, Terrence W. Starz, MD ABSTRACT. Piva SR, Fitzgerald GK, Irrgang JJ, Bouzubar F, Starz TW. Get Up and Go test in patients with knee osteoarthritis. Arch Phys Med Rehabil 2004;85: Objective: To determine the reliability, minimum detectable change (MDC), and validity of the Get Up and Go (GUG) test. Design: Repeated-measures test-retest for reliability. Correlational study for validity. Setting: Institutional practice. Participants: Convenience sample of 130 people, 105 with knee osteoarthritis (OA) (80 women; mean age, 62 9y) and 25 healthy controls (21 women; mean age, 57 8y). Interventions: Not applicable. Main Outcome Measures: Western Ontario and McMaster Universities Osteoarthritis Index, the Activity of Daily Living Scale of the Knee Outcome Survey, and the 8 scales of the Medical Outcomes Study 36-Item Short-Form Health Survey. Results: Intratester and intertester reliability was.95 (95% confidence interval [CI],.72.98) and.98 (95% CI,.94.99), respectively. The MDC, based on measurements by a single tester and between testers, was 1.5 and 1.2 seconds, respectively. Time to perform the GUG test was longer for persons with knee OA than it was for the controls (mean difference, 3.3s; 95% CI, ). Correlations between the GUG test and measures of physical function did not differ significantly from correlations between the GUG test and measures that do not specifically evaluate physical function. Conclusions: The GUG test is reliable and has an MDC that is adequate for clinical use. Validity of the GUG test as a single measure of physical function was not supported. Further research should include testing a battery of performance-based measures of physical function. Key Words: Knee; Osteoarthritis; Rehabilitation; Reliability and validity by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation THE GET UP AND GO (GUG) TEST is a performancebased measure of function that has been used with patients with knee osteoarthritis (OA) and with older persons in several clinical trials. 1-5 The GUG test described by Hurley et al 2 measures the time a person takes to get up from a chair and walk 50ft (15.2m) as fast as possible along a level and unobstructed corridor. This performance-based measure of physical From the Department of Physical Therapy, School of Health and Rehabilitation Science, University of Pittsburgh (Piva, Fitzgerald, Irrgang, Bouzubar); and Arthritis and Internal Medicine Associates, UPMC Health System (Starz), Pittsburgh, PA. Supported by the Western Pennsylvania Chapter of the Arthritis Foundation. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the author(s) or on any organization with which the author(s) is/are associated. Correspondence to Sara R. Piva, MS, PT, Dept of Physical Therapy, SHRS, University of Pittsburgh, Rm 6035, Forbes Tower, Pittsburgh, PA 15260, srpst24@pitt.edu. Reprints are not available from the author /04/ $30.00/0 doi: /j.apmr function requires an ability to rise from a seated position, walk, and maintain balance. Although self-reported measures of function are often primary endpoints for clinical outcome studies, several researchers 6-8 have suggested that performance-based measures should also be used. Their contention is that because the relationship between self-reported and performance-based measures of function is often only moderately strong, one may be measuring different aspects of the same construct In addition, because performance-based measures assess a person s ability to complete a task, whereas self-report measures assess one s perception of his/her ability to perform a task, it has been suggested that some people may not recognize a mild decline in physical function as being a problem and therefore that performance-based measures would identify decrements in physical function before self-reports. 13 Recent studies 8,11 have shown that performance-based measures identify limitations in physical function earlier and more frequently than do selfreported measures. To date, the validity of the GUG test as a measure of physical function in a population with knee OA has not been investigated. Validity is defined as the degree to which evidence and theory support the interpretation of test scores for a proposed use of the test. 14 Determining the validity of the GUG test is the most fundamental consideration in evaluating its usefulness as a measure of physical function of patients with knee OA. Providing evidence to support interpretation of the GUG test is the first step in establishing its usefulness as a performancebased measure of physical function for patients with knee OA. Therefore, that was the purpose of this study. We sought evidence that the GUG score is reliable, with minimal measurement error, and that it is related in a predictable manner to other measures of physical function in persons with knee OA. METHODS Participants Data for this study were obtained as part of a larger study from the Department of Physical Therapy, University of Pittsburgh, Pittsburgh, PA, that investigated muscle performance issues in persons with knee OA and in paired matched controls. People with knee OA were eligible to participate in this study if they had diagnoses of tibiofemoral or patellofemoral OA, if they were 45 years of age or older, if they met the 1986 American College of Rheumatology clinical and radiographic criteria for knee OA (ie, knee pain with osteophytes and at least 1 of the following: age 50y, morning stiffness 30min or crepitus with active motion of the knee, such as when squatting while weight bearing). 15,16 They must also have had grade II or greater Kellgren and Lawrence radiographic changes (ie, definitive evidence of at least minimal severity of 1 or more of the following radiologic features: formation of osteophytes, periarticular ossicles, narrowing of joint cartilage associated with sclerosis of subchondral bone, and small pseudocystic areas with sclerotic walls in the subchondral bone). 17 Exclusion criteria included previous total knee arthroplasty or a history of cardiovascular disease or uncontrolled hyper-

2 GET UP AND GO TEST AND KNEE OSTEOARTHRITIS, Piva 285 tension. Persons were included in the control group if they did not have a history of knee problems. Exclusion criteria for the control group were a history of cardiovascular disease or uncontrolled hypertension. All subjects who agreed to participate signed a consent form approved by the University of Pittsburgh Institutional Review Board for Biomedical Research. Overall, 130 people participated. Among them, 105 had knee OA (80 women) and 25 were in the control group (21 women), which was matched in age and gender with 25 randomly selected subjects from the sample of subjects with knee OA. Only the first 50 subjects (43 women) with knee OA were used to determine reliability. All subjects were used to provide evidence for validity of the GUG test. Procedures for the GUG Test To perform the GUG test, subjects were seated on a standard-height chair with armrests in front of a 20-m unobstructed corridor. The finish line was marked with a strip of tape placed 15.2m away from the front edge of the chair. Subjects were instructed to sit with their backs touching the back of the chair. On the command go, subjects stood and walked as fast as possible along the level corridor. They were instructed not to slow down before crossing the finish line. A stopwatch was used to measure in seconds the time from the command go until subjects crossed the finish line. The examiner stood at the finish line during the test. Subjects who used canes while walking were permitted to use them during the test. All subjects wore walking shoes. Procedures to Determine Test-Retest Reliability Two physical therapists collected data with which to estimate test-retest reliability. Before data were collected, examiners participated in a 30-minute training session to become familiar with testing procedures. To determine intratester reliability, the first 25 subjects with knee OA who entered the study were measured twice by the same examiner during a single testing session. To determine intertester reliability, the next 25 subjects with knee OA were measured twice by different examiners in the same testing session. Examiners were blinded to results of the other examiners measurements. The order of examiners was systematically alternated to avoid order effects. Subjects rested for 2 minutes between trials. Concurrent Measures of Function Concurrent patient-reported measures of physical, social, and emotional function included the Medical Outcomes Study 36-Item Short-Form Health Survey 18 (SF-36), the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index, 19 and the Activities of Daily Living Scale (ADLS) of the Knee Outcome Survey Item Short-Form Health Survey. The SF-36 is a general measure of health-related quality of life that consists of 36 items that measure 8 scales of health, including physical function, role limitations because of physical problems, role limitations from emotional problems, vitality, mental health, social functioning, bodily pain, and general health perception. 18 The scales are designed to capture the physical component summary and the mental component summary of health. Scores for each scale range from 0 to 100, with higher values indicating more optimal levels of health. The psychometric properties of the SF-36 are well established. 18,21,22 WOMAC Osteoarthritis Index. The WOMAC Osteoarthritis Index is a disease-specific health status measure. It explores clinically important, patient-relevant symptoms in the areas of pain, stiffness, and physical function in patients with hip and knee OA. 19 The WOMAC includes 5 items that measure pain, 2 items that measure stiffness, and 17 items that measure physical function. We used the Likert version of the WOMAC, in which each item was scored on a 5-point scale. Scores for each scale are created by summing the scores of the individual items composing the scale. Higher scores represent worse health status. Reliability and validity of the WOMAC has been established. 19,23 ADLS of the Knee Outcome Survey. The ADLS is a knee-specific measure of symptoms and physical function during activities of daily living (ADLs). The ADLS consists of 14 items that measure the full spectrum of symptoms and functional limitations during ADLs that one may experience as a result of a variety of knee pathologies. Each item is scored on a 6-point Likert-type scale, with higher values indicating better status. Psychometric testing has shown the ADLS to be reliable, valid, and responsive. 20,24 Data Management and Analysis Test-retest reliability. To estimate intratester reliability, we compared the consistency of GUG test scores collected by repeated measurement by a single physical therapist of the first 25 subjects. To estimate intertester reliability we compared the consistency of GUG scores by repeating the measurements on 2 occasions taken by 2 physical therapists of the second 25 subjects. We used the intraclass correlation coefficient (ICC 2,1 ) 25 to estimate intratester and intertester reliability. This model is appropriate when the unit of analysis is a single measurement and when repeated measures are a random selection from the larger universe of repeated measures. 25 The mean square estimates to calculate the ICC were obtained from a random effects 2-way analysis of variance with repeated measures. In this analysis, subjects and the repeated measures were considered random variables. The 95% confidence interval (CI) for the reliability values was calculated. 26 Measurement Error and Minimum Detectable Change Results of the reliability analyses were used to calculate the standard error (SE) of measurement and the minimum detectable change (MDC). The SE of measurement was calculated as SD (1 r), where r is the test-retest reliability coefficient and SD is the standard deviation of the scores. Some researchers 27,28 consider the SE of measurement to be the most appropriate statistic for determining statistically meaningful change of a health outcome measurement. A statistically meaningful level of change is the amount of change needed to be certain, within a defined level of statistical confidence, that the change that occurred was beyond that which would be the result of measurement error. 29 MDC was calculated as (SE of measurement). 30 In this formula, 1.96 is the standard normal score associated with a 2-tailed 95% CI and 2 is included to reflect that there is measurement error associated with both the first and second repeated measures when calculating test-retest reliability. Validity Two analyses were performed to provide evidence for validity. People with knee OA were expected to have lower physical function levels than individuals without knee OA. 5,31 Therefore, we hypothesized that the time taken to perform the GUG test would be longer for persons with knee OA than it would be for age- and gender-matched subjects without knee OA. To test this hypothesis, we performed a paired t test using the GUG data from the 25 randomly selected subjects with knee OA and from 25 persons with healthy knees who were

3 286 GET UP AND GO TEST AND KNEE OSTEOARTHRITIS, Piva Table 1: Demographics Characteristics of Subjects Who Participated in the Reliability Study Group Intratester Reliability Sample (n 25) Intertester Reliability Sample (n 25) Age (y) Height (cm) Weight (kg) NOTE. Values are mean SD. matched in age and gender to these randomly selected persons with knee OA. 26 In the second analysis, we hypothesized that the GUG test would be more strongly related to concurrent patient-reported measures of physical function than to measures that do not specifically measure physical function. More specifically, we hypothesized that the GUG test would correlate more highly with the WOMAC, ADLS, and the SF-36 physical function scale than with the SF-36 general health, social function, vitality, role limitations due to emotional problems, mental health, role limitations due to physical health problems, and bodily pain scales. We calculated Pearson correlation coefficients to test this hypothesis, using data from all 105 study subjects. We tested the equality of the correlations for nonindependent samples (unidirectional test,.05) with a t test statistic 32 to determine if correlations between the GUG test and the concurrent measures of physical function (WOMAC, ADLS, SF-36 physical function scale) differed significantly from correlations between the GUG and the concurrent measures that do not specifically measure physical function (general health, social function, vitality, role limitations due to emotional problems, mental health, role limitations due to physical health problems, bodily pain). RESULTS Demographic characteristics of the 50 subjects who participated in the reliability study are reported in table 1. The ICC for the intratester reliability was.95 (95% CI,.72.98) and the ICC for the intertester reliability was.98 (95% CI,.94.99). Corresponding values for the SE of measurement were.55 seconds and.42 seconds, based on repeated measurements for a single tester and 2 testers, respectively. The MDCs based on the SE of measurement for repeated measures by a single tester and by 2 testers were 1.5 and 1.2 seconds, respectively. Demographic characteristics of all 105 subjects in the validity study are reported in table 2. The WOMAC, ADLS, and SF-36 scores for all persons with and without knee OA are reported in table 3. The average time to complete the GUG test was seconds for the 25 randomly selected persons with knee OA and seconds for the 25 age- and gender-matched subjects without knee OA. The mean difference between these 50 Table 2: Demographic Characteristics of Subjects Who Participated in the Validity Study Group Subjects With Knee OA (n 105) Age- and Gender-Matched Control Subjects (n 25) Age (y) Height (cm) Weight (kg) NOTE. Values are mean SD. Table 3: Summary of the GUG Test, WOMAC, ADLS, and SF-36 Scores for Subjects With and Without Knee OA Group Control (n 25) Knee OA (n 105) GUG test (s) WOMAC ADLS SF-36 physical function SF-36 role physical SF-36 bodily pain SF-36 general health SF-36 vitality SF-36 social function SF-36 role emotional SF-36 mental health NOTE. Values are mean SD. people was 3.3 seconds (95% CI, ), which was significant (t 4.4, P.001). Pearson correlation values are reported in table 4, and results of the tests of equality of correlations for nonindependent samples are reported in table 5. Correlations of the GUG test with the WOMAC (r.39), ADLS (r.34), and SF-36 physical function scale (r.43) were higher than correlations between the GUG test and the other SF-36 scales. However, some differences between the correlations were not significant. For instance, the correlation between the GUG test and the SF-36 mental health scale did not differ statistically from the correlations between the GUG test and any of the other concurrent measures of physical function. The correlation between the GUG and ADLS did not differ statistically from the correlation between the GUG and bodily pain, general health, and emotional role scales of SF-36. DISCUSSION An important element of the validity to interpret test scores relies on the technical quality of a test. The technical quality of the GUG may include evidence of satisfactory score reliability and measurement error. 14 Poor reliability and high levels of measurement error limit the extent to which test results can be generalized beyond the particulars of a specific application of the measurement process and consequently reduce the usefulness and confidence that can be placed in a measurement. 14 This study has shown that the GUG test is reliable and acceptable for clinical use. Reliability refers to the consistency of a measurement to yield the same results when the testing Table 4: Pearson Product-Moment Correlation Values (r) Between the GUG Test and the WOMAC, ADLS, and the SF-36 Measurement r P WOMAC* ADLS* SF-36 physical function* SF-36 role physical SF-36 bodily pain SF-36 general health SF-36 vitality SF-36 social function SF-36 role emotional SF-36 mental health *Concurrent measures of physical function were used to test the validity of the GUG.

4 GET UP AND GO TEST AND KNEE OSTEOARTHRITIS, Piva 287 Table 5: Comparison of Relationships Between the GUG and Concurrent Measures of Physical Function and Measures That Did Not Directly Measure Physical Function Relationship of GUG With SF-36 GH SF-36 SF SF-36 Vitality SF-36 RE SF-36 MH SF-36 RP SF-36 BP WOMAC 1.67* 3.04* 3.19* 2.00* * 2.23* ADLS * 2.32* * 1.06* SF-36 PF 1.95* 3.32* 3.80* 2.11* * 2.3* NOTE. Values in cells are t statistics to compare the relationship between the GUG and the WOMAC, ADLS, 8 scales of SF-36, and the SF-36 physical and mental component scores. Abbreviations: BP, bodily pain; PF, physical function; GH, general health; MH, mental health; RE, role emotional; RP, role physical; SF, social function. *P.05. procedure is repeated on a specific population and the construct measured by the test has not changed Interpretation of the CIs around the ICC values leads to the conclusion that the true estimate of intratester reliability of the GUG is between.72 and.98 and that the true estimate of intertester reliability is between.94 and.99. Therefore, even considering the worse case scenario (lower bound of the 95% CI.72), the reliability of the GUG is still satisfactory for clinical use. Measurement error, determined in this study by calculating the SE of measurement and the MDC, refers to the hypothetical difference between an examinee s observed score on any particular measurement and the examinee s true score for the procedure. 14 Calculation of the SE and MDC provides a threshold for interpreting the GUG over time. The difference between the MDC values based on the SE of measurement for 1 tester (1.5s) and 2 testers (1.2s) was small (0.3s) and perhaps not clinically meaningful; therefore, to avoid the use of multiple values, we suggest that 1 MDC be chosen. To be more conservative and confident of the interpretation, we chose to use the larger MDC (that based on the SE within a single tester). Using this criterion, when the GUG score changes more than 1.5 seconds, one can be reasonably confident that true change has occurred, not just noise or measurement error. Knowledge of the MDC is essential when investigating the effect of interventions on change in performance-based measures of function in patients with knee OA. In addition to the technical quality of a test, different sources of evidence are needed to support the meaning and interpretation of a test score (ie, its validity). 14 Some types of evidence, such as that based on test content, relationships to other variables, and the consequences of testing, may all be critical to the use and interpretation of the GUG test. To provide evidence that the GUG test is a measure of physical function in patients with knee OA, we tested the following propositions: (1) if the construct tested with the GUG is an attribute of patients with knee OA, then we would expect the GUG scores to be greater in those with knee OA compared with those without knee OA; (2) if the content domain of the GUG is consistent with physical function, then we would expect the GUG test to be highly related to other valid measures of physical function that serve as the reference to test the GUG. Results of the first analysis used to provide evidence for interpretation of the GUG as a measure of physical function supported our hypothesis that individuals with knee OA would take longer to complete the GUG test than age- and gendermatched subjects without knee OA. This indicates that the construct measured by the GUG test appears to be an attribute of patients with knee OA. The second analysis showed that, although the GUG test had stronger correlations with concurrent measures of physical function than with the general health, social function, vitality, role limitations due to emotional problems, mental health, role limitations due to physical health, and bodily pain scales of the SF-36, the tests of the differences between these relationships were not significant for some of these correlations. Based on these results, the GUG test failed to show the hypothesized relationships with concurrent measures of physical, social, and emotional function. Based on results of the second analysis, the GUG by itself does not appear to be an adequate representation of patient-reported physical function. We believe that the inability to show the hypothesized relationships between the GUG test and concurrent measures of physical and emotional function may result from the narrow range of physical function represented by the GUG compared with the range of physical function measured by the WOMAC, ADLS, and the SF-36 physical functional scale. It seems that the GUG underrepresents the construct physical function. Construct underrepresentation refers to the degree to which a test fails to capture important aspects of the construct it purports to measure. 14 It implies a narrowed meaning of test scores, because the test does not adequately sample the content domain of physical function. 14 For example, the GUG underrepresents the content domain of physical function, as defined by patientreported measures of physical function, because it does not contain a sufficient variety of physical activities that are generally reported by patients with knee OA as being difficult. For example, the GUG test does not represent the ability to go up and down stairs, which is often difficult for persons with knee OA, and is a component of physical function as operationalized by the ADLS, WOMAC, and the SF-36 physical function scale. The contention of construct underrepresentation seems to be further supported by the relatively small correlation coefficients between the GUG test and the concurrent measures of physical function, with none accounting for more than 19% of the variance of the patient-reported measures of physical function we used in this study. Thus, a battery of performancebased measures of physical function is recommended to measure more comprehensively physical function in patients with knee OA. 36 Tasks that should be considered for inclusion are additional physical tasks such as going up and down stairs, squatting, getting in and out of a car, and lifting and carrying objects. A battery of performance-based tests would be more likely to measure comprehensively physical function through a wider range of ability. Further research is needed to establish standardized procedures for these tests and to provide evidence for their interpretation and usefulness as measures of physical function in subjects with knee OA. Results of this study should only be applied to patients with knee OA. Although the concept of construct underrepresentation may explain the low correlations between the GUG test and selfreported measures of physical function, other factors may also have influenced these findings. Some researchers have suggested that because performance-based measures assess one s

5 288 GET UP AND GO TEST AND KNEE OSTEOARTHRITIS, Piva ability to complete a task whereas self-report measures assess a person s perception of his/her ability to perform a task, some people may not recognize a mild decline in physical function as a problem. Therefore, performance-based measures might identify decrements in physical function before self-reports. 8,10-12 Based on clinical observation of the sample in this study, we speculate that the low correlations perhaps occurred because early decrements in strength, balance, and increased pain may affect the performance of the GUG at a time when the patients have not perceived any changes during daily activities. We observed that some subjects with knee OA reported high levels of physical function in self-reports, but needed longer times to perform the GUG. Extensive evidence has been provided to show that the WOMAC, ADLS, and the SF-36 physical function scale measure the construct of physical function. Some might argue that the bodily pain, general health, and the role physical scales of the SF-36, because they form together with the physical function scale the physical component summary of health of the SF-36, may also relate to physical function. However, note that the physical function, role physical, bodily pain scales, and to a smaller degree the general health scales, all have been shown to be valid measures of overall physical health, not physical function. The interpretation of each scale has been shown to differ markedly, as verified from the factor-analytic studies of their construct validity. 37 The physical functioning scale evaluates the limitations in several types of physical activities, from dressing and bathing to the most vigorous types of physical activities, and has been shown to be the best all-around measure of physical health. However, the bodily pain scale evaluates how such pain limits one s activities, the role physical scale evaluates problems with work and daily activities as a result of physical health, and the general health scale evaluates the overall health and the individual s health expectation. 37 Therefore, we believe that the use of the bodily pain, general health, and the role physical scales of the SF-36 as measures of other than physical function was appropriate. Furthermore, some may disagree with our use of the 8 scales of the SF-36 as 8 distinct measures rather than in the aggregate as when combined in the physical and mental component scores, whereas for the WOMAC instrument, we used the total score rather than the individual physical function, pain, and stiffness subscales. The reason for using the total score of the WOMAC is that, among the 5 items of the pain subscale, 4 items question how much pain the patient has during walking, managing stairs, standing, and sitting, all of which are considered physical function activities. In effect, these same 4 physical activities that help to form the pain subscale are also used in the questions that form the physical function subscale. Within that subscale, the questions are related to the degree of difficulty the patient has in performing each of the abovementioned physical activities. Therefore, because the pain and physical function subscales of the WOMAC seem to overlap, we believe that the use of the total WOMAC score reflects better the construct physical function. CONCLUSIONS The GUG test had sufficient reliability for clinical use. Additional evidence is needed to support its use as a single measure of physical function. Further research should consider development and testing of a battery of performance-based measures of physical function to measure more comprehensively the construct of physical function. Acknowledgment: We thank the University of Pittsburgh Medical Center Arthritis Network Registry for assistance with subject recruitment for this study. References 1. Fisher NM, Gresham G, Pendergast DR. Effects of a quantitative progressive rehabilitation program applied unilaterally to the osteoarthritic knee. Arch Phys Med Rehabil 1993;74: Hurley MV, Scott DL, Rees J, Newham DJ. Sensorimotor changes and functional performance in patients with knee osteoarthritis. Ann Rheum Dis 1997;56: Hurley MV, Scott DL. Improvements in quadriceps sensorimotor function and disability of patients with knee osteoarthritis following a clinically practicable exercise regime. Br J Rheumatol 1998; 37: Bearne LM, Scott DL, Hurley MV. Exercise can reverse quadriceps sensorimotor dysfunction that is associated with rheumatoid arthritis without exacerbating disease activity. Rheumatology (Oxford) 2002;41: Jette AM, Lachman M, Giorgetti MM, et al. Exercise it s never too late: the strong-for-life program. Am J Public Health 1999; 89: Fried LP, Bandeen-Roche K, Williamson JD, et al. Functional decline in older adults: expanding methods of ascertainment. J Gerontol A Biol Sci Med Sci 1996;51:M Fried LP, Bandeen-Roche K, Chaves PH, Johnson BA. Preclinical mobility disability predicts incident mobility disability in older women. J Gerontol A Biol Sci Med Sci 2000;55:M Brach JS, VanSwearingen JM, Newman AB, Kriska AM. Identifying early decline of physical function in community-dwelling older women: performance-based and self-report measures. Phys Ther 2002;82: Cress ME, Schechtman KB, Mulrow CD, Fiatarone MA, Gerety MB, Buchner DM. Relationship between physical performance and self-perceived physical function. J Am Geriatr Soc 1995;43: Elam JT, Graney MJ, Beaver T, el Derwi D, Applegate WB, Miller ST. Comparison of subjective ratings of function with observed functional ability of frail older persons. Am J Public Health 1991;81: Rozzini R, Frisoni GB, Ferrucci L, Barbisoni P, Bertozzi B, Trabucchi M. The effect of chronic diseases on physical function. Comparison between activities of daily living scales and the Physical Performance Test. Age Ageing 1997;26: Sager MA, Dunham NC, Schwantes A, Mecum L, Halverson K, Harlowe D. Measurement of activities of daily living in hospitalized elderly: a comparison of self-report and performance-based methods. J Am Geriatr Soc 1992;40: Reuben DB, Valle LA, Hays RD, Siu AL. Measuring physical function in community-dwelling older persons: a comparison of self-administered, interviewer-administered, and performancebased measures. J Am Geriatr Soc 1995;43: Joint Committee on Standards for Educational and Psychological Testing of the American Educational Research Association, American Psychological Association. National Council on Measurement in Education. Standards for educational and psychological testing. Washington (DC): American Educational Research Association; Altman R, Asch E, Bloch D, et al. Development of criteria for the classification and reporting of osteoarthritis. Classification of osteoarthritis of the knee. Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Arthritis Rheum 1986;29: Altman RD. Criteria for classification of clinical osteoarthritis. J Rheumatol 1991;27(Suppl): Kellgren JH, Lawrence JS. Radiological assessment of osteoarthrosis. Ann Rheum Dis 1957;16: McHorney CA, Ware JE Jr, Raczek AE. The MOS 36-Item Short-Form Health Survey (SF-36): II. Psychometric and clinical tests of validity in measuring physical and mental health constructs. Med Care 1993;31: McConnell S, Kolopack P, Davis AM. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC): a review

6 GET UP AND GO TEST AND KNEE OSTEOARTHRITIS, Piva 289 of its utility and measurement properties. Arthritis Rheum 2001; 45: Irrgang JJ, Snyder-Mackler L, Wainner RS, Fu FH, Harner CD. Development of a patient-reported measure of function of the knee. J Bone Joint Surg Am 1998;80: McHorney CA, Ware JE Jr, Lu JF, Sherbourne CD. The MOS 36-item Short-Form Health Survey (SF-36): III. Tests of data quality, scaling assumptions, and reliability across diverse patient groups. Med Care 1994;32: Ware JE Jr, Sherbourne CD. The MOS 36-item short form health survey (SF-36): I. Conceptual framework and item selection. Med Care 1992;30: Bellamy N, Watson-Buchanan W, Goldsmith CH, Campbell J. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1998;15: Marx RG, Jones EC, Allen AA, et al. Reliability, validity, and responsiveness of four knee outcome scales for athletic patients. J Bone Joint Surg Am 2001;83: Shrout PE. Measurement reliability and agreement in psychiatry. Stat Methods Med Res 1998;7: Simel DL, Samsa GP, Matchar DB. Likelihood ratios with confidence: sample size estimation for diagnostic test studies. J Clin Epidemiol 1991;44: Lydick E, Epstein RS. Interpretation of quality of life changes. Qual Life Res 1993;2: Wyrwich KW, Wolinsky FD. Identifying meaningful intra-individual change standards for health-related quality of life measures. J Eval Clin Pract 2000;6: Nunnally JC, Bernstein IH. Psychometric theory. New York: McGraw-Hill; Portney LG, Watkins MP. Foundations of clinical research: applications to practice. Stamford: Appleton & Lange; Felson DT. The epidemiology of knee osteoarthritis: results from the Framingham Osteoarthritis Study. Semin Arthritis Rheum 1990;20(3 Suppl 1): Olkin I, Siotani M. Asymptotic distribution functions of a correlation matrix. Stanford: Stanford Univ Laboratory for Qualitative Research in Education; Kirshner B, Guyatt G. A methodological framework for assessing health indices. J Chronic Dis 1985;38: Kopec JA, Esdaile JM. Functional disability scales for back pain. Spine 1995;20: Guyatt GH, Kirshner B, Jaeschke R. Measuring health status: what are the necessary measurement properties? J Clin Epidemiol 1992;45: Ettinger WH Jr, Burns R, Messier SP, et al. A randomized trial comparing aerobic exercise and resistance exercise with a health education program in older adults with knee osteoarthritis. The Fitness Arthritis and Seniors Trial (FAST). JAMA 1997;277: Ware JE Jr. SF-36 health survey update. Spine 2000;25: