A news story in Nature Medicine (14, 1133; 2008) discusses an investigation into the publication status of the clinical-trials literature (PLoS Med., doi: 10.1371/journal.pmed.0050191; 2008), which concludes that positive results of clinical trials for drugs
http://blogs.nature.com/peer-to-peer/2008/11/positive_skew_of_clinicaltr...

