Medical research answers many questions about health, illness, and treatment options. Evaluating new medicines and other treatments may involve research using randomized controlled trials. In such trials the participants who receive the treatment under study are assigned at random (by chance, like the flip of a coin). This is necessary to ensure that the outcomes are determined only by the treatment under study and not by other factors that could otherwise influence treatment assignment. Other participants who, by the randomization process, serve as controls receive a standard treatment or placebo treatment (a pill or procedure that does not include active ingredients). The March 24/31, 2010, issue of JAMA includes a review article about clinical trials. This Patient Page is based on one previously published in the June 21, 2006, issue of JAMA.