A group of researchers from Canada set up a study to compare the most commonly used scales of pain and disability. They tested a group of 132 chronic whiplash pain patients using the same tests over a six week period of time.
The tests were given before treatment and then six weeks later. Some patients were only given advice and followed up by telephone. Others followed an individualized six-week long exercise program.
The best measure of change in disability was the Patient-Specific Functional Scale (PSFS). It is quick and easy to use with patients. It's a valid and reliable tool. And it is responsive in measuring clinically important changes.
The SF-36 is still a good overall measure of fitness, general health, and includes disability and pain. Many clinics use this tool along with others such as the PSFS that target more specific measures.