Many patients with chronic musculoskeletal pain suffer associated functional limitations in work capacity and personal productivity. However, pain differs among patients and is quite difficult to measure. Although some validity lies in an individual's reports of pain, no generally accepted measurements are applicable between individuals. On a scale of 0 to 10, changes in pain that a patient reports are valid only with respect to that person. However, what constitutes one person's rating of 10 may represent only 5 or 6 to another person, so pain rating scales have only a limited role in assessing impairment.