VALIDATION DATA

The WOMAC is available in over 80 alternate language forms.

Cronbach's alphas for the Likert Scale format of the WOMAC were 0.86-0.89, 0.90-0.91, and 0.95 for the pain, stiffness, and function subscales, respectively.

Cronbach's alphas for the Visual Analog format were 0.7.-0.81 for pain and 0.89-0.91 for function (not calculated for the stiffness subscale) 

Kendall's TAU-C:  for Likert Scale formats were 0.68, 0.48, and 0.68 for pain, stiffness, and function subscales, respectively, and 0.68 for the total score;  for the Visual Analog format: 0.64, 0.61, 0.72, and 0.64

Intraclass correlation coefficients (ICC's): 0.74-0.95, 0.58-0.90, and 0.92, for pain, stiffness, and physical function subscales, respectively

Overall, test-retest reliability of the WOMAC pain subscale has been variable across studies but generally meets the minimum standard; test-retest reliability has been more consistent and stronger for the physical function subscale, but the stiffness subscale has shown low test-retest reliability.

Development of the WOMAC involved expert opinion (including rheumatologists and epidemiologists), reviews of existing instruments, and surveys of patients with hip and / or knee OA 

The factor structure of the WOMAC has been confirmed in some studies of patients with hip and knee OA.

However, one study of patients with hip and knee OA awaiting arthroplasty failed to support a single-item solution for the pain subscale. Other studies have shown that items on the physical function subscale did not load unequivocally on that factor, and some items from the pain and physical function subscales tended to load together on a factor. High correlations and overlapping items between the pain and physical function subscales may pose measurement problems: it has been argued that the ability of the WOMAC physical function scale to detect change may be particularly limited in situations where there is a low correlation or “mismatch” between physical function and pain severity