File drawer problem

In applied statistics, the file drawer problem results from the fact that academics tend not to publish results that indicate the null hypothesis could not be rejected. That is, they got a statistically non-significant result that failed to find the relationship they were looking for. Even though these papers can often be interesting, they tend to end up unpublished, in "file drawers."

For example, suppose that around the world 20 studies are done to assess whether vitamin C prevents some disease. If vitamin C has no such effect, then in only 5% of those studies, i.e. only one of the 20, some measure statistic would be expected to exceed a critical value. If only that study is published, it looks as if vitamin C is effective. If all 20 are published, the opposite conclusion appears. Thus the file drawer problem biases the published conclusions against the null hypothesis that vitamin C is ineffective.