Responsiveness of the SF-36 and WOMAC following periacetabular osteotomy for acetabular dysplasia.

BACKGROUND: Periacetabular osteotomy is a relatively common reconstructive procedure for the adolescent or young adult with acetabular dysplasia. Although several measures have been used to characterize the outcome, the responsiveness of these measures in this population has not been determined. The purpose of this study was to estimate the responsiveness of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Short Form-36 (SF-36) in patients with acetabular dysplasia treated with periacetabular osteotomy. METHODS: Eighty-three patients with acetabular dysplasia treated with periacetabular osteotomy between 2000 and 2005 completed the WOMAC and SF-36 both preoperatively and postoperatively. The scores on each domain of these outcome measures were calculated and analyzed to determine the parameters of responsiveness, including the minimal detectable change at the 90% confidence level. RESULTS: The mean duration of follow-up was 1.9 years. Comparison of the effect size, standardized response mean, and minimal detectable change for the SF-36 and WOMAC demonstrated that the WOMAC was more sensitive to change than the SF-36 was, particularly in the physical function domain (minimal detectable change, 9.1) and the pain domain (minimal detectable change, 5.5). Only one of the eight domains of the SF-36, bodily pain, demonstrated a change in outcome that exceeded the minimal detectable change, which was 2.38. CONCLUSIONS: Both the WOMAC and the SF-36 demonstrated adequate responsiveness to change over time in patients with acetabular dysplasia treated with periacetabular osteotomy, although the WOMAC was more sensitive to change. These results indicate that the WOMAC is sufficiently responsive to be used as a joint-specific measure for assessing changes following periacetabular osteotomy for the treatment of acetabular dysplasia.

A functional difficulty and functional pain instrument for hip and knee osteoarthritis.

INTRODUCTION: The objectives of this study were to develop a functional outcome instrument for hip and knee osteoarthritis research (OA-FUNCTION-CAT) using item response theory (IRT) and computer adaptive test (CAT) methods and to assess its psychometric performance compared to the current standard in the field. METHODS: We conducted an extensive literature review, focus groups, and cognitive testing to guide the construction of an item bank consisting of 125 functional activities commonly affected by hip and knee osteoarthritis. We recruited a convenience sample of 328 adults with confirmed hip and/or knee osteoarthritis. Subjects reported their degree of functional difficulty and functional pain in performing each activity in the item bank and completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Confirmatory factor analyses were conducted to assess scale uni-dimensionality, and IRT methods were used to calibrate the items and examine the fit of the data. We assessed the performance of OA-FUNCTION-CATs of different lengths relative to the full item bank and WOMAC using CAT simulation analyses. RESULTS: Confirmatory factor analyses revealed distinct functional difficulty and functional pain domains. Descriptive statistics for scores from 5-, 10-, and 15-item CATs were similar to those for the full item bank. The 10-item OA-FUNCTION-CAT scales demonstrated a high degree of accuracy compared with the item bank (r = 0.96 and 0.89, respectively). Compared to the WOMAC, both scales covered a broader score range and demonstrated a higher degree of precision at the ceiling and reliability across the range of scores. CONCLUSIONS: The OA-FUNCTION-CAT provided superior reliability throughout the score range and improved breadth and precision at the ceiling compared with the WOMAC. Further research is needed to assess whether these improvements carry over into superior ability to measure change.

A computer-adaptive disability instrument for lower extremity osteoarthritis research demonstrated promising breadth, precision, and reliability.

OBJECTIVE: To develop and evaluate a prototype measure (OA-DISABILITY-CAT) for osteoarthritis research using item response theory (IRT) and computer-adaptive test (CAT) methodologies. STUDY DESIGN AND SETTING: We constructed an item bank consisting of 33 activities commonly affected by lower extremity (LE) osteoarthritis. A sample of 323 adults with LE osteoarthritis reported their degree of limitation in performing everyday activities, and completed the Health Assessment Questionnaire-II (HAQ-II). We used confirmatory factor analyses to assess scale unidimensionality and IRT methods to calibrate the items and examine the fit of the data. Using CAT simulation analyses, we examined the performance of OA-DISABILITY-CATs of different lengths compared with the full-item bank and the HAQ-II. RESULTS: One distinct disability domain was identified. The 10-item OA-DISABILITY-CAT demonstrated a high degree of accuracy compared with the full-item bank (r=0.99). The item bank and the HAQ-II scales covered a similar estimated scoring range. In terms of reliability, 95% of OA-DISABILITY reliability estimates were over 0.83 vs. 0.60 for the HAQ-II. Except at the highest scores, the 10-item OA-DISABILITY-CAT demonstrated superior precision to the HAQ-II. CONCLUSION: The prototype OA-DISABILITY-CAT demonstrated promising measurement properties compared with the HAQ-II, and is recommended for use in LE osteoarthritis research.

Performance-based or self-report measures of physical function: which should be used in clinical trials of hip fracture patients?

OBJECTIVES: To assess the validity, sensitivity to change, and responsiveness of 3 self-report and 4 performance-based measures of physical function: activity measure for postacute care (AM-PAC) Physical Mobility and Personal Care scales, the Medical Outcomes Study 36-Item Short Form Health Survey Physical Function scale (SF-36 PF), the Physical Functional Performance test (PFP-10), the Short Physical Performance Battery (SPPB), a 4-meter gait speed, and the six-minute walk test (6MWT). DESIGN: A prospective observational study of patients after a hip fracture. Assessments were performed at baseline and 12 weeks postenrollment. SETTING: Inpatient and outpatient rehabilitation facilities in Norway, the United Kingdom, Sweden, Israel, Germany, the United States, Denmark, and Spain. PARTICIPANTS: A sample of study participants (N=108) who had a hip fracture. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Assessments of validity (known-groups, concurrent, construct, and predictive), sensitivity to change (effect size, standardized response mean [SRM], SE of measure, minimal detectable change (MDC), and responsiveness (optimal operating cut-points and area under the curve) between baseline and 12-week follow-up. RESULTS: All physical function measures achieved comparably acceptable levels of validity. Odds ratios in predicting patient Global Assessment of Improvement at 12 weeks were as follows: AM-PAC Physical Mobility scale, 5.3; AM-PAC Personal Care scale, 3.6; SF-36 PF, 4.3; SPPB, 2.0; PFP-10, 2.5; gait speed, 1.9; and 6MWT, 2.4. Effect sizes and SRM exceeded 1 SD for all 7 measures. Percent of patients who exceeded the MDC(90) at week 12 were as follows: AM-PAC Physical Mobility scale, 90%; AM-PAC Personal Care scale, 74%; SF-36 PF, 66%; SPPB, 36%; PFP-10, 75%; gait speed, 69%; and 6MWT, 75%. When evaluating responsiveness using the area under receiver operating curves for each measure, all measures had acceptable responsiveness, and no pattern emerged of superior responsiveness depending on the type of measure used. CONCLUSIONS: Findings reveal that the validity, sensitivity, and responsiveness of self-report measures of physical function are comparable to performance-based measures in a sample of patients followed after fracturing a hip. From a psychometric perspective, either type of functional measure would be suitable for use in clinical trials where improvement in function is an endpoint of interest. The selection of the most appropriate type of functional measure as the primary endpoint for a clinical trial will depend on other factors, such as the measure's feasibility or the strength of the association between the hypothesized mechanism of action of the study intervention and a functional outcome measure.

Creating a computer adaptive test version of the late-life function and disability instrument.

BACKGROUND: This study applied item response theory (IRT) and computer adaptive testing (CAT) methodologies to develop a prototype function and disability assessment instrument for use in aging research. Herein, we report on the development of the CAT version of the Late-Life Function and Disability Instrument (Late-Life FDI) and evaluate its psychometric properties. METHODS: We used confirmatory factor analysis, IRT methods, validation, and computer simulation analyses of data collected from 671 older adults residing in residential care facilities. We compared accuracy, precision, and sensitivity to change of scores from CAT versions of two Late-Life FDI scales with scores from the fixed-form instrument. Score estimates from the prototype CAT versus the original instrument were compared in a sample of 40 older adults. RESULTS: Distinct function and disability domains were identified within the Late-Life FDI item bank and used to construct two prototype CAT scales. Using retrospective data, scores from computer simulations of the prototype CAT scales were highly correlated with scores from the original instrument. The results of computer simulation, accuracy, precision, and sensitivity to change of the CATs closely approximated those of the fixed-form scales, especially for the 10- or 15-item CAT versions. In the prospective study, each CAT was administered in <3 minutes and CAT scores were highly correlated with scores generated from the original instrument. CONCLUSIONS: CAT scores of the Late-Life FDI were highly comparable to those obtained from the full-length instrument with a small loss in accuracy, precision, and sensitivity to change.