The more active a research area is, the less reliable its results are.

John Ioannidis suggested popular areas of research publish a greater proportion of false results in his paper Why most published research findings are false. Of course popular areas produce more results, and so they will naturally produce more false results. But Ioannidis is saying that they also produce a greater proportion of false results.

Now Thomas Pfeiffer and Robert Hoffmann have produced empirical support for Ioannidis’s theory in the paper Large-Scale Assessment of the Effect of Popularity on the Reliability of Research. Pfeiffer and Hoffmann review two reasons why popular areas have more false results.

First, in highly competitive fields there might be stronger incentives to “manufacture” positive results by, for example, modifying data or statistical tests until formal statistical significance is obtained. This leads to inflated error rates for individual findings: actual error probabilities are larger than those given in the publications. … The second effect results from multiple independent testing of the same hypotheses by competing research groups. The more often a hypothesis is tested, the more likely a positive result is obtained and published even if the hypothesis is false.

In other words,

In a popular area there’s more temptation to fiddle with the data or analysis until you get what you expect. The more people who test an idea, the more likely someone is going to find data in support of it by chance.

The authors produce evidence of the two effects above in the context of papers written about protein interactions in yeast. They conclude that “The second effect is about 10 times larger than the first one.”

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