"Why Most Published Research Findings Are False"

In fact, the origin of the statistic is an earlier paper by the same author, John PA Ioannidis, Contradicted and Initially Stronger Effects in Highly Cited Clinical Research. Journalistic coverage of the later paper quotes a description of the earlier:

“Five out of six epidemiological studies have been contradicted in a very short period of time,” says Ioannidis, “while about one out of three randomized clinical trials were also refuted.”

Note that this is not 1/3 of all randomized studies, but just the highly cited ones, the ones that have any chance of an attempt at replication (and still 25% have no published attempt). It is not obvious to me whether these studies will be higher or lower quality than average. ETA: actually, there is a "control group" of articles published in the same prestigious journals, but with fewer citations. They are contradicted a little less often, p<.1, and not because people aren't bothering to replicate them.