This paper by the Center for International Development (CID), uses sales data on HIV/AIDS drugs in a sample of 34 low and middle income countries between 1995 and 1999 to assess empirically the impact of patents on unsubsidized access to a new drug therapy. The main finding is that patent rights do have a negative effect on unsubsidized access to HIV/AIDS drugs. Between 1995 and 1999, switching all HIV/AIDS drugs from a patent regime to a no patent regime would have actually increased access to therapy at least by 30%.