Registered clinical trials make positive findings vanish
It seems that the main issue here is that with pre-registration, study authors have to pick a single measure of primary benefit at the outset, whereas before, they <i>might</i> have made that choice after getting results back. The original study is at PLoSONe, and it is not a difficult read[1]. From that source:<p>>>Prior to 2000, investigators had a greater opportunity to measure a range of variables and to select the most successful outcomes when reporting their results... Among the 25 preregistered trials published in 2000 or later, 12 reported significant, positive effects for cardiovascular-related variables other than the primary outcome.<p>That is, in most cases, there are large effects for some outcome, and if they get to choose the primary outcome after looking at some results, they could have been cherry-picking the outcome variables.<p>[1] <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132382" rel="nofollow">http://journals.plos.org/plosone/article?id=10.1371/journal....</a>