1,174 primary outcomes appearing in 82 metaanalyses published in health-related biological and behavioral research sampled from the Web of Science categories Genetics & Heredity and Psychiatry and measured how individual results deviated from the overall summary effect size within their respective meta-analysis.
whose outcome included behavioral parameters were generally more likely to report extreme effects, and those with a corresponding author based in the US were more likely to deviate in the direction predicted by their experimental hypotheses, particularly when their outcome did not include additional biological parameters.
Although this latter finding could be interpreted as a publication bias against non-US authors, the US effect observed in behavioral research is unlikely to be generated by editorial biases. Behavioral studies have lower methodological consensus and higher noise, making US researchers potentially more likely to express an underlying propensity to report strong and significant findings.
...A complete explanation would probably invoke a combination of cultural, economic, psychological, and historical factors, which at this stage are largely speculative. Our preferred hypothesis is derived from the fact that researchers in the United States have been exposed for a longer time than those in other countries to an unfortunate combination of pressures to publish and winner-takes-all system of rewards (20, 22). This condition is believed to push researchers into either producing many results and then only publishing the most impressive ones, or to make the best of what they got by making them seem as important as possible, through post hoc analyses, rehypothesizing, and other more or less questionable practices (e.g., 10, 13, 22, 26). Such a pattern of modulating forces may gradually become more prevalent also in other countries currently and in the near future (18, 20, 21)."
"And Fanelli was also quick to point out that this kind of exaggeration doesn’t seem to be exclusive to the U.S.
The US are an ideal subject because they are relatively homogeneous and yet very big and scientifically productive, so it was easy for us to compare the US to the rest of the world. And of course the US-effect was especially interesting, since it helped us exclude classic explanations, such as editorial biases and simple file-drawer effects. But we suspect that with higher statistical power we would observe specific biases in other countries, in Europe and elsewhere, possibly limited to specific fields and periods in time.
Science is a struggle for truth against methodological, psychological, and sociological obstacles."