Authors: Khanna, Dinesh; Furst, Daniel; Wong, Weng; Tsevat, Joel; Clements, Philip; Park, Grace; Postlethwaite, Arnold; Ahmed, Mansoor; Ginsburg, Shaari; Hays, Ron

Source: Quality of Life Research, Volume 16, Number 6, August 2007 , pp. 1083-1092(10)

Publisher: Springer

Abstract:

ObjectivesTo evaluate the reliability and validity and estimate the minimally important difference (MID) for the SF-6D in patients with systemic sclerosis (SSc). Subjects We used data from two clinical studies to analyze the SF-6D in patients with SSc: Study 1 was a cross-sectional observational study (N = 107) designed to assess three direct preference measures—the rating scale, time trade-off, and standard gamble (SG) in patients with diffuse SSc and limited SSc, and Study 2 was a 12-month randomized, placebo-controlled, clinical trial (N = 168) assessing oral bovine collagen versus placebo in diffuse SSc. Methods We assessed the test-retest reliability of the SF-6D in Study 2 over a mean (SD) 4.8 (3.0)-week interval and the agreement between the SF-6D and direct preference measures in Study 1 using intraclass correlations (ICC). The MID was estimated using three different anchors—the SF-36 change in health item (patients who answered “somewhat better” formed the MID group), the Health Assessment Questionnaire-Disability Index (HAQ-DI; change of ≥0.14 and ≥0.22) and the skin score (change of ≥5.3). Results The mean (SD) SF-6D scores were 0.61 (0.12) in Study 1 and 0.64 (0.13) in Study 2. Test-retest reliability for the SF-6D was high (ICC = 0.82 [95% CI: 0.76, 0.87]). Agreement between the SF-6D and three direct preferences measures was poor to moderate (0.16-0.52). The MID estimate for the SF-6D using the change in SF-36 item −0.012 and this level of change was similar to the no change group. The mean MID estimate for the SF-6D improvement using the HAQ-DI and skin score as anchors was 0.035 (effect size of 0.27). Conclusion This is the first study to assess the SF-6D in SSc. The SF-6D is reliable and valid in patients with SSc. We provide MID estimates that can aid in calculating sample size for clinical trials involving patients with diffuse SSc.

Keywords: Systemic sclerosis; Scleroderma; SF-6D; Utility measures; Preference-based measures; Minimally important difference

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s11136-007-9207-3

Affiliations: 1: Email: dinesh.khanna@uc.edu

Publication date: 2007-08-01

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