VALIDATION DATA

The SF-36 VT is available in over 120 languages

For the SF-36 VT, Cronbach's α was 0.84 to 0.88 over three time points in patients with RA (n = 631), whereas in patients with OA (n = 62), all SF-36 domains, including the SF-36 VT, had a Cronbach's α of 0.75 to 0.94

In one OA study (n = 62; mean age 58 years, 2 to 10 years post arthroplasty), 4-week test-retest reliability of the SF-36 VT was r = 0.92; in contrast, another OA study found very poor 1-week stability at r = 0.03 (n = 21; mean age 70 years). In patients with RA (n = 150), the ICC for the SF-36 VT was excellent (0.91; 95% CI 0.86-0.94) over 2 weeks

The SF-36 VT covers both energy and fatigue, but these may not be opposite ends of a single continuum. Thus, although a person who is not fatigued would score 0 out of 100 on a scale containing four fatigue items, they could potentially score 50 on the SF-36 VT by answering no to both the energy and fatigue items because of a lack of energy rather than the presence of fatigue. In an RA study, the SF-36 version 2 VT items loaded across the following two separate factors: “full of life” and “lot of energy” loaded on a factor with items of feeling happy, peaceful, and healthy, whereas “feel tired” and “worn out” loaded on a factor with items of feeling down and feeling sad (n = 401)

In patients with RA (n = 86), the SF-36 VT correlated strongly with disability (r = 0.56) and weakly to moderately with physician global assessment, patient global assessment, pain, tender joints, and inflammatory markers (−0.27 to −0.37); its correlation with anxiety, depression, and helplessness is reported as 0.28 to 0.50 (n = 229). The SF-36 VT discriminated between patients with RA with low versus moderate DAS28 but not between those with moderate versus high DAS28 (n = 200)