According to a survey conducted by Roper Starch Worldwide for the American Pain Society in 1999, "Chronic pain as defined by this study is a severe and ever present problem. It can be as much of a problem to middle age adults as seniors and is one women are more likely to face than men. The majority of chronic pain sufferers have been living with their pain for over 5 years. Although the more common type is pain that flares up frequently versus being constant, it is still present on average almost 6 days in a typical week.
"About one third of all chronic sufferers describe their pain as being almost the worst pain one can possibly imagine. Their pain is more likely to be constant than flaring up frequently and two-thirds of them have been living with it for over 5 years."

Source

Roper Starch Worldwide, Inc., "Chronic Pain In America: Roadblocks To Relief," research conducted for the American Pain Society, the American Academy of Pain Medicine and Janssen Pharmaceutica, Jan. 1999.