It could be an example of publication bias, from the wiki article on effect size [1]: An example of this is publication bias, which occurs when scientists repo

It could be an example of publication bias, from the wiki article on effect size [1]: An example of this is publication bias, which occurs when scientists report results only when the estimated effect sizes are large or are statistically significant. As a result, if many researchers carry out studies with low statistical power, the reported effect sizes will tend to be larger than the true (population) effects, if any. [1] https://en.wikipedia.org/wiki/Effect_size https://en.wikipedia.org/wiki/Effect_size