Lisa Feldman Barrett in The New York Times:
An initiative called the Reproducibility Project at the University of Virginia recently reran 100 psychology experiments and found that over 60 percent of them failed to replicate — that is, their findings did not hold up the second time around. The results, published last week in Science, have generated alarm (and in some cases, confirmed suspicions) that the field of psychology is in poor shape. But the failure to replicate is not a cause for alarm; in fact, it is a normal part of how science works. Suppose you have two well-designed, carefully run studies, A and B, that investigate the same phenomenon. They perform what appear to be identical experiments, and yet they reach opposite conclusions. Study A produces the predicted phenomenon, whereas Study B does not. We have a failure to replicate. Does this mean that the phenomenon in question is necessarily illusory? Absolutely not. If the studies were well designed and executed, it is more likely that the phenomenon from Study A is true only under certain conditions. The scientist’s job now is to figure out what those conditions are, in order to form new and better hypotheses to test.
A number of years ago, for example, scientists conducted an experiment on fruit flies that appeared to identify the gene responsible for curly wings. The results looked solid in the tidy confines of the lab, but out in the messy reality of nature, where temperatures and humidity varied widely, the gene turned out not to reliably have this effect. In a simplistic sense, the experiment “failed to replicate.” But in a grander sense, as the evolutionary biologist Richard Lewontin has noted, “failures” like this helped teach biologists that a single gene produces different characteristics and behaviors, depending on the context.