1. Merskey, H., and Bogduk, N., 1994, Classification of Chronic Pain, Second Edition, IASP Task Force on Taxonomy (Merskey, H., and Bogduk, N., eds.), IASP Press, Seattle, pp. 209–214.
2. Harstall, C., and Ospina, M., 2003, How prevalent is chronic pain? Pain: Clinical Updates Vol. XI, No.2.
3. Verhaak, P.F.M., Kerssens, J.J., Dekker, J., Sorbi, M.J., Bensing, J.M., 1998, Prevalence of chronic benign pain disorder among adults: a review of the literature. Pain 77: 231–239.
4. Kloke, M., Rapp, M., Bosse, B., Kloke, O., 2000, Toxicity and/or insufficient analgesia by opioid therapy: risk factors and the impact of changing the opioid. A retrospective analysis of 273 patients observed at a single center. Supportive Care in Cancer 8: 479–486.
5. Goudas, L.C., Carr, D.B., Bloch, R., Balk, E., Ioannidis, J.P.A., Terrin, N., Gialeli-Goudas, M., Chew, P., Lau, J., October 2001, Management of cancer pain. Volume 1 and 2. Evidence Report/Technology Assessment No. 35, Agency for Healthcare Research and Quality (AHRQ) Publication No. 02-E002.