A comparison of different indices of responsiveness.

The first purpose of this study was to determine if different indices of responsiveness provided similar rank orderings of scales in terms of responsiveness. The second purpose was to compare the responsiveness of patient-specific, disease-specific, and generic health status measures for patients undergoing total hip arthroplasty. All patients of one surgeon at a single institution were eligible for the study. Patients who did not speak English or did not return for post-operative evaluations were excluded. Patients completed two disease-specific scales (the Harris Hip Scale and the Western Ontario and McMaster osteoarthritis scale or WOMAC), one generic health status scale (the SF-36), and two patient-specific scales (the McMaster-Toronto Arthritis questionnaire or MACTAR and the Patient Specific Index or PASI). All scales were administered on two occasions: before and 6 months after total hip arthroplasty. Responsiveness was measured using: (1) the responsiveness statistic; (2) standardized response mean; (3) relative efficiency statistic; (4) effect size; and also by (5) correlating each scale's change score with the change in patients' global ratings of their "hip function." Seventy-eight sequential patients completed the study. The mean age was 62 years (range 25-87), 55% were male, and 71% had osteoarthritis. Test-retest reliability of the scales ranged from 0.31 to 0.93. The correlation among scales was consistent with a priori hypotheses confirming construct validity of the scales. Although the disease-specific scales were generally rated as the most responsive scales, the different indices provided different rank orderings by up to 5 levels (p = 0.04). In conclusion, disease-specific scales are the most responsive scales. However, choosing among scales based on responsiveness must be done with caution because different indices of responsiveness provide different rank ordering.