Pain is the most common reason for seeking medical care and the third leading cause of
physical impairment in the United States. One in three people in the U.S. suffers from
some form of chronic pain; ~ 50 million Americans are partially or totally disabled by
chronic pain. In the United Kingdom, an estimated 8 million people suffer from chronic or
persistent pain. Between 30% and 90% of surgical patients experience moderate or severe
postoperative pain.