1. Mäntyselkä P, Kumpusalo E, Ahonen R, Kumpusalo A, Kauhanen J, Viinamaki H, et al. Pain as a reason to visit the doctor: a study in Finnish primary health care. Pain. 2001;89:175–80.
2. Jones RBNCL, Gass D, Grol R, Mant D, Silagy C. The nature of primary medical care. London: Oxford University Press; 2003.
3. Health and Social Care Information Centre. Prescription Cost Analysis England 2006. http://www.hscic.gov.uk/catalogue/PUB01307 . 2007.
4. Wilcox CM, Cryer B, Triadafilopoulos G. Patterns of use and public perception of over-the-counter pain relievers: focus on nonsteroidal antiinflammatory drugs. J Rheumatol. 2005;32:2218–24.
5. Federal Interagency Forum on Aging Related Statistics. Older Americans 2012: Key Indicators of Well-Being. Washington, DC: US Government Printing Office; 2012. http://www.agingstats.gov/agingstatsdotnet/Main_Site/Data/Data_2012.aspx .