John Sutter is the author of a recent paper in the Economic Journal titled, The Power of Bias in Economics. He looked at 159 topics that had been subjected to such evidence synthesis and found they were all underpowered. It's very common to see an exaggeration of two-fold or about 30% or a third would be inflated by four-fold he says.
John Ioannidis of Stanford University talks with EconTalk host Russ Roberts about his research on the reliability of published research findings. They discuss Ioannidis's recent study on bias in economics research, meta-analysis, the challenge of small sample analysis, and the reliability of statistical significance as a measure of success in empirical research.