The Short Form-36 is Preferable to the SIP as a Generic Health Status Measure in. Patients Undergoing Elective Total Hip Arthroplasty.

Transcription

1 The Short Form-36 is Preferable to the SP as a Generic Health Status Measure in Patients Undergoing Elective Total Hip rthroplasty.~ ~~~ Gerold Stucki, Matthew H. Liang, Charlotte Phillips, Jeffrey N. Katz Objective. To assess the comparative usefulness of the Short Form-36 [SF-36) and the Sickness mpact Profile (SP) as generic health status measures in total hip arthroplasty. Methods. nalysis of preoperative and %month data of 54 consecutive patients undergoing total hip replacement for osteoarthritis or rheumatoid arthritis. nstruments were mailed to patients preoperatively and 3 months postoperatively. Results. n 10 of the 12 SP subscales, but just 1 of the 8 SF-36 subscales, more than 40% of the patients had scores of zero. On a 100-point scale, the median global SP was 12 (range 0-40) whereas the median global SF-36 was 50 [range 10-85). This indicates that Gerold Stucki, MD, MS, Lecturer in Rheumatology, Physical Medicine, and Rehabilitation, Department of Rheumatology and Physical Therapy, University of Zurich, Switzerland Matthew H. Liang. MD, MPH, ssociate Professor of Medicine, Departments of Medicine and Rheumatology/mmunology, Charlotte Phillips, MPH, Research ssociate, Multipurpose rthritis and Musculoskeletal Disease Center, and Jeffrey N. Katz, MD, MS, ssistant Professor of Medicine, Department of Rheumatology/mmunology, Brigham and Women's Hospital, Harvard Medical School, Boston, M. Supported by NH grant R Dr. Stucki is recipient of a fellowship from the Swiss Science National Foundation and grants from the EULR and the Swiss ssociations of Physical Medicine, Rehabilitation, and Rheumatology. Dr. Katz is supported in part by an rthritis nvestigator ward from the rthritis Foundation. ddress correspondence to Gerold Stucki, MD, MS, Rheumaklinik und nstitut fur Physikalische Therapie, Universitatsspital, Gloriastrasse 25, CH-8091 Zurich, Switzerland. Submitted for publication February 1, 1995; accepted in revised form March 28, by the merican College of Rheumatology. 174 many items of the SP were not germane to patients undergoing joint arthroplasty. The global and, particularly, the physical dimensions of the SF-36 were more responsive than their SP counterparts, as measured both by the standardized response mean (1.26 and 0.88, respectively) and the correlation with self-perceived improvement in quality of life (r = 0.37 and 0.26, respectively). The SF-36, but not the SP, discriminated between patients with relatively good physical performance at 3 months with respect to their ability to work, to play sports, or to garden. Conclusion. The SF-36 is briefer, more relevant, and more responsive than the SP and is preferable as a generic health status measure in patients undergoing elective hip arthroplasty. The SF-36 should be tested in other populations as well as other conditions to determine whether it is a superior generic health status instrument for evaluative research in orthopedic surgery. Key words: Hip arthroplasty; Joint surgery; Health status; Short Form-36; Sickness mpact Profile; Outcome assessment. NTRODUCTON The merican and European orthopedic communities have reached consensus on the broad outcome domains that should be assessed in the evaluation of total hip arthroplasty [1,2]. These include physical examination of the hip, assessment of clinical complications, radiographic studies, and disease-specific and generic health status as reported by the patient. Thus, development of generic health status instruments measuring physical, psychological, and social health /95/$5.00

2 rthritis Care and Research Health Status in Hip rthroplasty 175 is a major advance in the evaluation of orthopedic measurement. Generic instruments complement disease-specific measures of hip impairment, such as the Harris Hip Score (3) or the Hip-Rating Questionnaire (4), and permit comparison of the impact upon quality of life of orthopedic versus non-orthopedic conditions. variety of generic health status instruments, such as the Sickness mpact Profile (SP) (5,6), the Functional Status Questionnaire (7), the ndex of Well-Being, the Nottingham Health Profile (81, and the Short Form-36 (SF-36)(9,10), have been used in orthopedic studies. Each has been shown to be reliable and valid. While small differences in responsiveness to change have been documented among instruments, no instrument has been shown to be superior (11-13). The utility of an instrument for research involves consideration of several criteria. First, the questions asked should be relevant to the condition under study. One intuitive measure of relevance is congruence between the questionnaire items and the questions asked by the physician or the complaints described by patients who have the target problem. Second, an instrument should be able to detect clinically meaningful improvement in all subsets of patients. Third, measurement properties of the instrument should not be subject to a ceiling or floor effect; that is, for patients with good initial health status, improvement on the measure should be possible, and for patients with poor initial status, deterioration on the measure should be possible. Fourth, the instrument should be as short as possible. Brevity and relevance optimize completeness of responses and retention of subjects in longitudinal evaluation. The SF-36 contains 36 questions, and is as responsive as longer measures used in total joint arthroplasty (13). Since its introduction in 1988 it has become one of the most widely used generic health-status instruments and has been translated and validated in many languages. The SP, one of the original generic measures, has been used in numerous studies of total hip arthroplasty (6,12,14) and is one of the most responsive instruments used to measure the impact of joint arthroplasty on quality of life (11-13). The objective of this study was to compare the relevance, face validity, and evaluative properties of the SF-36 versus the SP in patients undergoing total hip arthroplasty. PTENTS ND METHODS Study design and patients. Consecutive patients scheduled for elective primary or revision total hip replacement were recruited from the Brigham and Women s Hospital from mid-march to mid-ugust Data collection and measures. nstruments were sent to patients by mail preoperatively and 3 months postoperatively. The SF-36 has 36 multiple-choice questions aggregated into 8 subscales, and it takes about 5 minutes to complete. t measures physical functioning, role limitation due to physical health problems, bodily pain, general health, vitality, social functioning, role limitation due to emotional problems, and mental health. uthors of the SF-36 have not published algorithms for calculating a global score. To facilitate comparison of instruments, we calculated a global score for the SF-36 as the unweighted mean of all subscale scores (13). The SP contains 136 questions answered in a yes/ no format and takes minutes to complete. Each item is weighted. The instrument has 12 subscales, 7 of which are aggregated into 2 dimensions, physical and psychosocial. global score is calculated as the weighted sum of all items. The SP has no pain dimension. Both scales are scored from 0 to 100. However, perfect health is represented by 0 with the SP and by 100 with the SF-36. To facilitate the comparison between the instruments, we subtracted the SP score from 100. Three months postoperatively, patients were asked about their self-perceived improvement in overall quality of life (no improvement, little or moderate, great, or greater improvement than was dreamed possible), satisfaction with the result of surgery (very satisfied, somewhat satisfied, somewhat dissatisfied, or very dissatisfied], ability to participate in sports and to work (not limited, slightly, moderately, greatly, or totally limited because of the hip), and ability to do gardening/yardwork (easily, with difficulty, or cannot do). nalyses. Nonparametric statistics were used throughout because SP scores were not distributed normally. To assess whether the SF-36 and the SP measure similar constructs, we examined correlations between the instruments and their respective physical and psychological dimensions, using Spearman s rank correlation coefficient. To assess the number of relevant items within each instrument, we examined the median score of the SF- 36 and the SP at baseline. More difficulty is reflected by a higher median score on both scales. We further compared the number of patients who had difficulty with items in the physical subscales of each instrument

3 176 Stucki et al Vol. 8, No. 3, September 1995 Table 1. Demographic and clinical features of the 54 study patients Feature Female ge, mean (SD) Race (n = 53) White Black Other Employment status (n = 52) Employed full-time Employed part-time Homemaker Unemployed or retired Education [n = 53) Did not complete high school High school graduate, no college Some college Diagnosis Osteoarthritis Rheumatoid arthritis Other Revision arthroplasty NO. [% of patients 36 (67) 60 ( (25) 9 (17) 5 (10) 25 (48) (30) 30 (57) ) 7 (13) 10 (19) 10119) and the number of patients with zero scores on each subscale. The responsiveness of the SF-36, the SP, and their respective physical dimensions was evaluated using the standardized response mean (SRM; the ratio of mean change in score divided by the standard deviation of change) (11). higher SRM indicates greater responsiveness. Other measures of responsiveness were correlations of the change scores with 2 external criteria, self-perceived improvement in quality of life and satisfaction with the result of surgery (15). We assumed that successful surgery would be associated with patient satisfaction and increased health-related quality of life; therefore, higher correlation indicates greater responsiveness. To assess ceiling effects, we counted the number of perfect scores at baseline and at 3 months and examined whether the scores clustered close to the unimpaired end of the scales. We assumed that few, if any, patients would have normal function prior to surgery, since a common indication for joint arthroplasty is functional loss due to end-stage arthritis (16). Based on preliminary 6-month data showing that more than half of such patients have some difficulty with walking and transfers (17), we expected few perfect scores and a wide distribution of scores at 3 months. n particular, we expected that many patients would still be limited in their ability to do demanding activities, such as playing sports or gardening (14). To assess floor effects, we counted the number of perfect scores at baseline and at 3 months and examined whether the scores clustered close to the disabled end of the scales. RESULTS Patients. One hundred six patients who met eligibility criteria during the 5-month study period were invited to participate. Of these, 19 patients refused, 14 agreed but did not complete the preoperative forms, SF ! ; SP Figure 1. Scatter plot of the Sickness mpact Profile (SP) and Short Form-36 (SF-36) scores of the 54 patients at baseline (0 = worst possible score; 100 = perfect health), illustrating the wider spread of patients along the SF-36 than along the SP scale and the clustering of SP values at the lower end of the scale. (No scores were higher than 40 on the SP thus, the scale has been shortened for space considerations.]

4 rthritis Care and Research Health Status in Hip rthroplasty 177 Table 2. Numbers of patients with normal baseline scores on each instrument NO. (70) of NO. (70) of patients patients with perfect with perfect SP subscale SF-36 subscale Sickness mpact profile scores Short Form-36 scores (SP) (n = 54) (SF-36) (n = 54) Global score 2 (41 Global score 0 (0) Subscale scores Subscale scores Physical 3 (61 Physical 0 (0) mbulation 6 (11) Role physical 11 (20) Mobility 26 (48) Body care and movement 6 (11) Psychological 16 (30) Psychological 2 (4) Social interaction 26 (48) Role emotional 32 (59) lertness behavior 38 (70) Communication 45 (83) Emotional behavior 22 (41) Eating 35 (65) Pain 1(2) Recreation 14 (26) Energy 0 (0) Home maintenance 5 19) Social activity 16 (30) Sleep and rest 8 (15) Health perceptions 0 (0) Work 24 ( did not complete postoperative forms, and 4 canceled their operations. Thus a total of 54 patients gave complete preoperative and postoperative data. The demographic and clinical characteristics of the study sample are presented in Table 1. The mean age was 60 years and 67% were women. Sixty-nine percent of the patients underwent arthroplasty procedures for osteoarthritis; 19% of the procedures were revisions. Ninety-two percent were unilateral procedures, 6% bilateral, and 2% (1 patient) a combined hip and knee replacement. The patients who did not complete the protocol differed only in that they were somewhat older (mean age 64 versus 60 years] and included more men (46% versus 33%) than the study sample. nalyses. The Spearman rank correlations between the SF-36 and the SP were 0.78 for the global instrument, 0.67 for the physical dimension, and 0.70 for the psychological dimension. The strength of these relationships (all significant at P < 0.01) indicates that the instruments and their subscales measure similar domains. Relevance of questionnaires. The median global SP score was 12 on the 100-point scale, with scores ranging from 0 to 40. This indicates that many items of the SP were not relevant to patients undergoing joint arthroplasty. n contrast, the median SF-36 score was 50 on the 100-point scale, with a range of Figure 1 shows the scatter plot of SP and SF-36 scores of individual patients at baseline. The SF-36 and SP scores were highly correlated (r = 0.76, P < O.O1]. However, there was a much wider spread of patients along the SF-36 than along the SP scale. SP values clustered at the lower end of the scale. Table 2 shows the number of patients with normal baseline scores on the subscales of each instrument. More than 50% of the patients had scores of 0 at baseline (no limitation on any single scale item) on 3 of the 12 SP subscales, and more than 40% of the patients scored 0 on 7 of the 12 SP subscales, including mobility, social interaction, alertness behavior, communication, emotional behavior, eating, and work. n contrast, more than 40% of the patients scored 0 on only 1 of the 8 SF-36 subscales, the emotional role scale. Table 3 shows the number of patients with difficulty on the ambulation and mobility scales of the SP and the physical function scale of the SF-36. Between 49% and 100% of the patients had difficulty performing each specific task of the physical function scale of the SF-36. On the other hand, between 0% and 63% could not perform tasks of the ambulation and mobility scales of the SP. For 14 of the 22 items in these 2 SP scales, less than 20% of the patients could not perform the task; for 6 other items, between 20% and 50% could

5 178 Stucki et a1 Vol. 8, No. 3, September 1995 Table 3. Numbers of patients with difficulty on individual items of the physical function scale of the Short Form-36 (SF-36) and the ambulation and the mobility scales of the Sickness mpact Profile [SP) before total hip arthroplasty Not 70 of Limited Limited limited patients a lot a little at all answering (TO) (TO) (70) yes SF-36 Physical Function scale Vigorous activities, such as running, lifting heavy objects, participating in strenuous sports Moderate activities, such as moving a table, pushing a vacuum cleaner, bowling, or playing golf Lifting or carrying groceries Climbing several flights of stairs Climbing one flight of stairs Bending, kneeling, or stooping Walking more than a mile Walking several blocks Walking one block Bathing and dressing yourself SP Mobility scale am getting around only within one building stay within one room am staying in bed more am staying in bed most of the time am not now using public transportation stay home most of the time am only going to places with restrooms nearby am not going into town stay away from home only for brief periods of time do not get around in the dark or in unlit places without someone s help SP mbulation scale walk shorter distances or stop to rest often do not walk up or down hills use stairs only with mechanical support; for example, handrail, cane, crutches walk up or down stairs only with assistance from someone else get around in a wheelchair do not walk at all walk by myself but with some difficulty; for example, limp, wobble, stumble, have a stiff leg walk only with help from someone go up and down stairs more slowly; for example, one step at a time, stop often do not use stairs at all get around only by using a walker, crutches, cane, walls, or furniture walk more slowly not perform tasks. Only 2 items were difficult for more than 50% of the patients. These findings demonstrate that the SF-36 contains more difficult items, including 1 item which all patients found difficult to perform. The SP, however, has more items of minor difficulty that were not important for many patients in this population. Because of these characteristics, there is more room for improvement on the physical dimension of the SF-36 than on the ambulation and mobility scales of the SP. This may explain the more favorable responsiveness of the SF- 36 as compared to the SP (Table 4). The responsiveness of the SF-36 and the SP are shown in Table 4. To provide perspective on the mag-

6 rthritis Care and Research Health Status in Hip rthroplasty 179 Table 4. Comparison of the ability of the Short Form-36 (SF-36) and the Sickness mpact Profile (SP] to measure change over time SP SF-36 Concept Question Method Global Physical Global Physical Relevance Responsiveness Ceiling Floor How many items are relevant for the most important physical subscales? How many subscales are relevant? Which instrument shows the best improvement in scores? Which instrument correlates best with selfperceived improvement in quality of life? (ref. 15) Do patients cluster at the normal end of the scale? Does instrument discriminate health status for those patients with scores close to the end (good health] of the scale? Do patients cluster at the worse end of the scale? Number of items endorsed by >SO% of the patients at baseline. Number of scales with <40% of the patients having normal scores. Standardized response mean (mean change/ standard deviation; ref Spearman s rank correlation. Distribution; number of patients with best possible score. Correlation with a clinically relevant external criterion for patients with scores close to the end of the scale. Distribution; number of patients with worst possible score. N mbulation and Mobility N Physical Function 1 of 22 9 of 10 5 of 12 3 of 3 7 of 8 2of * 0.45t 0.37t Clustering at 3 months; 4 patients with perfect global SP and 8 with perfect physical SP scores No correlation with ability to do work, gardening, or sports (among quartile of patients with best scores at 3 months] No clustering; no patients with worst possible score No clustering; no patients with the best possible score Correlation with the ability to do work, gardening, or sports (among quartile of patients with best scores at 3 months)$ No clustering; no patients with worst possible score * P < t P < $- r = 0.50 for work; r = 0.79 for gardening; r = 0.88 for sports. nitude of SRMs observed in this study, it has been suggested that an SRM of 0.2 represents a small intervention effect, 0.5 a moderate, and 0.8 or greater a large effect Thus, the global and physical SRMs observed for both instruments are quite large. The global and the physical dimensions of the SF-36 were more responsive than the equivalent SP scales, as measured both by the SRM (P = 0.05 between the physical, but not between the global, dimension] (13) and by the correlation with self-perceived improvement in quality of life (Table 4). This indicates that the SF-36 and its physical dimension are superior to the SP in discriminating patients according to selfreported improvement in quality of life following total hip arthroplasty. Ceiling effects. Both instruments had less than 2 patients with a normal score at baseline. Three of the 54 patients had normal baseline scores on the physical dimension of the SP but not on the SF-36 (Table 2). t 3 months, the scores of the SP and of its physical dimensions clustered in the lower end of the scale; 4 patients had a SP score of zero (normal) and 8 had a physical SP score of zero. However, these patients appeared to have limitations by other measures. For example, none of these patients worked without limitation: 3 patients reported light, 3 moderate, and 2 great limitation in work activities. For these patients, there was no significant rank correlation between their work ability and the SP (r = -0.04). There was, however, a moderately strong and borderline-significant rank correlation between the ability of these patients to work and the SF-36 (r = 0.50, P = 0.10). Similarly, for the quartile of patients (n = 81 with the best SP scores, the rank correlation between the SP and ability to participate in sports was r = 0.0 and between SP and the ability to do gardening/yardwork was r = (n = 12). There was, however, a strong rank correlation between the SF-36 and these activities (sports r = 0.88,

7 180 Stucki et ol Vol. 8, No. 3, September 1995 P < 0.01; gardening/yardwork r = 0.79, P < 0.01). This indicates that the SF-36, but not the SP, discriminated between patients with relatively good physical performance at 3 months. Floor effect. There were no patients with the worst possible score on either instrument at baseline or at 3 months. DSCUSSON Measurement of overall health status is an integral part of comprehensive orthopedic outcome assessment (2). The principal criteria for the selection of an optimal generic health status instrument are relevance, face validity, brevity, and responsiveness to clinical change (19). We chose to compare the SF-36 and SP among the many options available. The SF-36 has been translated and validated in many languages, allowing for studies across cultures and countries (ZO), and has become the most widely used generic health status instrument for many diseases, allowing for comparisons across diseases and conditions. The SP has been the most widely used generic instrument in published orthopedic studies (14,21-23), and therefore might be considered a standard against which newer instruments should be compared. We have shown that the SF-36 and its dimensions correlate highly with the respective dimensions of the SP. The responsiveness of the instruments global scores was similar, while the physical dimension of the SF-36 was more responsive than the physical dimension of the SP. The SP demonstrated a ceiling effect, while the SF-36 did not, and the SF-36 was able to detect differences in patients ability to do work, gardening, or sports at 3 months, while the SP was not. The favorable measurement properties of the SF- 36 in this surgical population may be partly explained by its physical dimension, which can discriminate among and between patients with a wide spectrum of activities, from vigorous activities such as running or participating in a strenuous sport to limitations with bathing and dressing. lthough the SP discriminates among patients with low to moderate physical activities, it does not discriminate among patients with a relatively high level of physical performance. The only questions that refer to such activities are walking up and down hills, using public transportation, or climbing stairs. lso, the yes/no format of the SP allows for less variation in ability than the 3 response categories used in the SF-36 (great, a little, no difficulty]. Surgical outcomes studies require long-term follow- up, typically at 3, 6, and 12 months and then at yearly intervals (2). For this reason, practical aspects such as the length of the instrument and the relevance of the items to the population under study are of great importance with respect to feasibility, response rate, and costs. lthough we did not measure the actual time required to complete the instruments, the SF-36 with 36 questions appears to require less time to complete than the SP with 136 questions. Because some SP dimensions that were not included in the SF-36, such as eating and communication, are not relevant in patients undergoing total hip arthroplasty, the shorter instrument is no less comprehensive. n exception may be sleep disturbance, a frequent problem for these patients, which is addressed by the SP but not the SF-36. t should be emphasized, however, that neither the SP nor the SF-36 is a gold standard for measuring health status. Both (as well as other instruments not included in this comparison) have specific advantages and disadvantages which make them more appropriate or less appropriate for a particular setting. lthough we found the SF-36 to be preferable in a population of patients undergoing elective hip arthroplasty, this does not imply superiority of the SF-36 over the SP in all circumstances. The SP may be better suited than the SF-36 for evaluating a relatively sick population with general deterioration of physical and psychological health or important comorbidity. Whereas the least difficult item of the physical dimension of the SF-36 is bathing and dressing yourself, the physical dimension of the SP includes items such as do not walk at all, am staying in bed most of the time, or get around in a wheelchair, which target a lower range of function. lso the SP includes scales addressing self-care, such as body care and movement. These observations suggest the SP may detect changes in lower levels of physical function that the SF-36 would miss. n our population most patients improved, and we could not examine floor phenomena. Particularly in patients undergoing joint arthroplasty for hip fractures, who generally have worse health status than patients undergoing elective surgery, the SF-36 may not be the preferred generic measure. The same may be true for the outcome assessment of revision or resection arthroplasty. The preferred instrument of these and other clinical situations remains to be defined. The SF-36 may prove to be the preferred instrument for many ambulatorytreated conditions of the lower extremity and spine. The objective of our study was to compare the instruments abilities to measure change over a wide range of disability. Thus, we deliberately included a heterogeneous group of patients with osteoarthritis and

8 rthritis Care and Research Health Status in Hip rthroplasty 181 rheumatoid arthritis and patients undergoing primary or revision arthroplasty. However, because of the relatively small sample size, meaningful analysis of these subsets was not possible. n addition, we obtained data on about half of the eligible patients, and noted differences in age and sex between our sample and the nonparticipants. These differences are unlikely to influence the specific arguments of this paper. However, these differences and the heterogeneity of our population warn that these data should be used cautiously, if at all, by clinicians and policy makers for evaluating the effectiveness of total hip arthroplasty. We conclude that the SF-36 is briefer, more relevant, and more responsive than the SP and is preferable as a generic health status measure in patients undergoing elective hip arthroplasty. The SF-36 should be tested in other populations as well as other conditions to determine whether it is a superior generic health status instrument for evaluative research in orthopedic surgery. We would like to thank Susanne Stucki, MEd, for assistance with the preparation of the manuscript. REFERENCES 1. Johnston RC, Fitzgerald RH jr, Harris WH, Poss R, Muller ME, Sledge CB: Clinical and radiographic evaluation of total hip replacement: a standard system of terminology for reporting results. J Bone Joint Surg 72: , Liang MH, Katz JN, Phillips C, Sledge C, Cats-Baril W: The total hip arthroplasty outcome evaluation form of the merican cademy of Orthopaedic Surgeons. J Bone Joint Surg 73: , Harris WH: Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty: an end-result study using a new method of result evaluation. J Bone Joint Surg 51: , , Johanson N, Charlson ME, Szatrowski TP, Ranawat CS: self-administered hip-rating questionnaire for the assessment of outcome after total hip replacement. J Bone Joint Surg 74: , Bergner M, Bobbitt R, Pollar WE, et al: The Sickness mpact Profile: validation of a health status measure. Med Care 14:57-67, Bergner M, Bobbitt R, Carter WB, Gilson BS: The Sickness mpact Profile: development and final revision of a health status measure. Med Care 19: , Jette M: Functional status instrument: reliability of a chronic disease evaluation instrument. rch Phys Med Rehabil61: , Hunt SM, McKenna S, McEwen J, Williams J, Papp E: The Nottingham Health Profile: subjective health status and medical consultations. Social Sci Med , Ware JE Jr, Sherbourne CD: The MOS 36-item Short- Form Health Survey (SF-36).. Conceptual framework and item selection. Med Care 30: , McHorney C, Ware JE Jr, Lu JFR, Sherbourne CD: The MOS 36-item Short-Form Health Survey (SF-36) Tests of data quality, scaling assumptions, and reliability across diverse patient groups. Med Care , Liang MH, Larson MG, Cullen KE, Schwartz J Comparative measurement efficiency and sensitivity of five health status instruments for arthritis research. rthritis Rheum 28: Liang MH, Fossel H, Larson MG: Comparisons of five health status instruments for orthopedic evaluation. Med Care 28: , Katz LN, Larson MB, Phillips CB, Fossel H, Liang MH: Comparative measurement sensitivity of short and longer health status instruments. Med Care 30: , Laupacis, Bourne R, Rorabeck C, Feeny D, Wong C, Tugwell P, Leslie K, Bullas R: The effect of elective total hip replacement on health-related quality of life. J Bone Joint Surg , Deyo R Measuring the functional status of patients with low back pain. rch Phys Med Rehabil 69: , Harris WH, Sledge CB: Total hip and total knee replacement (first of two parts). N Engl J Med 323: , Britz P, Whitley D, Venglish C, Kwoh CK: Patients expectations versus actual outcomes in total joint replacement (abstract). rthritis Care Res 3:Sll, Cohen J: Statistical power analyses for the behavioral sciences. New York, cademic Press, Liang MH, Katz JN: Measurement of outcome in rheumatoid arthritis. Baillieres Clin Rheumato16:23-37, Ware JE Jr: SF-26 Health Survey: Manual and nterpretation Guide. The Health nstitute, New England Medical Center, Boston, M, Deyo R: Comparative validity of the Sickness mpact Profile and shorter scales for functional assessment in low-back pain. Spine 11: , Deyo R, Diehl K: Measuring physical and psychosocial function in patients with low back pain. Spine 8: , Stucki G, Liang MH, Lipson SJ, Fossel H, Katz JN: Contribution of neuromuscular impairment to physical functional status in patients with lumbar spinal stenosis. J Rheumatol 21: , 1994