This month over 100 medical journals around the world are inviting readers to send information on unpublished trials. This amnesty should have important benefits for patients. Why?

Reports of properly conducted randomised controlled trials are the foundation of effective health care, but many are not submitted for publication.^{1 2} This reduces the power of systematic reviews to detect moderate but clinically important treatment effects. Patients may thus be denied effective forms of health care. A second problem is that since trials that show more promising effects are more likely to be submitted, research syntheses can give misleading conclusions about effectiveness. Patients may thus …