Confirmation bias occurs when an individual looks for and uses the information to support their own ideas or beliefs. It also means that information not supporting their ideas or beliefs is disregarded.
Confirmation bias often happens when we want certain ideas to be true. This leads individuals to stop gathering information when the retrieved evidence confirms their own viewpoints, which can lead to preconceived opinions (prejudices) that are not based on reason or factual knowledge. Individuals then pick out the bits of information that confirm their prejudices.
Confirmation bias has a long history. In 1620, Francis Bacon described confirmation bias as: “Once a man’s understanding has settled on something (either because it is an accepted belief or because it pleases him), it draws everything else also to support and agree with it. And if it encounters a larger number of more powerful countervailing examples, it either fails to notice them, or disregards them, or makes fine distinctions to dismiss and reject them, and all this with much dangerous prejudice, to preserve the authority of its first Conceptions.” (Bacon 1620)
In 2015, the former president of the National Lipid Association advocated for statin use in the elderly (Toth 2015) He cited one RCT of statin therapy (the PROSPER study), which reported a reduction in cardiovascular events in the elderly. However, he ignored the other published RCT of statins in older patients (CORONA), which reported no significant reduction in cardiovascular events (Dubroff 2017)
Mendel and coworkers investigated whether confirmation bias among doctors and medical students leads to poor diagnostic accuracy. He found that 13% of psychiatrists and 25% of students showed confirmation bias when searching for new information after having made a preliminary diagnosis. These participants were significantly less likely to make the correct diagnosis.
The impact of confirmation bias can be at the level of the individual all the way up to institution level. DuBroff showed that confirmation bias influenced expert guidelines on cholesterol and was highly prevalent when conflicts of interests were present (DuBroff 2017). He found that confirmation bias occurred due to a failure to incorporate evidence, or through misrepresentation of the evidence, which had the potential to skew guideline recommendations
Methods to avoid confirmation bias include rigorous protocols for searching for and reporting relevant information.
As opposed to literature reviews, systematic reviews search for, appraise and where relevant summarise the results of ALL available relevant evidence on a particular research question. Following a protocol for executing the literature searches and pre-specifying inclusion and exclusion criteria can avoid confirmation bias.
Editorial review of papers submitted for publication should include consideration of whether the authors have been biased in their inclusion or reporting of information relevant to their research study (of any kind). In addition, taking account of conflicts of interest is important to prevent confirmation bias.