The WOMAC (Western Ontario and McMaster Universities osteoarthritis index) is a self-administered questionnaire of disease severity specifically for people with osteoarthritis of the hip or knee [Bellamy, 2001]. It produces an aggregate total score, and scores for three sub-scales: pain, stiffness, and physical functioning/disability. For every question people rate their pain, stiffness, or function as none (score 0), mild (1), moderate (2), severe (3), or extreme (4). Thus, a higher score for each subscale corresponds to a worse condition.

The pain subscale includes five questions on the degree of pain experienced with certain positions and activities (for example, sitting or lying), with the subscore varying from 0 to 20.

The function subscale includes 17 questions on the degree of difficulty experienced while completing activities (for example, descending stairs), with the subscore varying from 0 to 68.

The stiffness subscale includes two questions on severity of stiffness (that is, after first awakening, and later in the day), with the subscore varying from 0 to 8.

WOMAC does not define what would be considered to be a clinically meaningful change. Reductions of 20%, 50% and 70% from baseline WOMAC scores have been suggested and assessed as appropriate goals for treatment [Bellamy et al, 2005].