10 Types of Study Bias

File Drawer Bias
On the flip side, scientists may relegate negative or neutral findings from clinical trials to a file drawer. blackred/Getty Images

In some ways, this is the flip side of publication bias. Negative results from a study get shoved in a metaphorical file drawer instead of being published. Critics see it as a particular problem when it comes to studies of new medications, which these days often are sponsored by the companies that developed them [source: Pannucci and Wilkins].

File-drawer bias can be significant. A study published in the New England Journal of Medicine in 2008 compared the results of published studies on antidepressants to data from a U.S. Food and Drug Administration registry of research that included unpublished information. It found that 94 percent of the published studies reported drugs having positive effects. But when the unpublished studies were included, the number with positive results dropped to 51 percent [source: Turner, et al.].

In an effort to get more information into the public domain, Congress in 2007 passed a law requiring researchers to report results of many human studies of experimental treatments to ClinicalTrials.gov. In 2016, the U.S. Food and Drug Administration strengthened the rules, requiring more thorough reporting of clinical trials, including drugs and devices that were studied but never brought to market [source: Piller].

But some critics worry that the laws won't have much teeth since there is no increase in enforcement staffing.

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