POST - Parliamentary Office of Science and Technology

Unintentional Bias in Forensic Investigation

Published Thursday, October 1, 2015

A short paper describing how cognitive biases can influence the results of forensic investigations.

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There are a number of unintentional reasoning errors that people systematically make, called cognitive biases. Several research studies have shown that these biases (some of which are highlighted below) can affect the results of investigations carried out by forensic examiners. This paper discusses how these biases might be mitigated.

  • Contextual bias occurs when irrelevant contextual information aboutan event, or the way in which some information is presented, influences reasoning. People are affected by information which has nothing to do with the actual decision at hand.
  • Confirmation bias occurs when people interpret information, or look for new evidence, in a way that conforms to their pre-existing beliefs or assumptions. People more easily see and give more weight to information which is consistent with what they already believe, and are less likely to see and give less weight to information which is not consistent with what they already believe.
  • Expected frequency bias occurs when people get used to a particular result occurring at a certain rate, and expect it to keep on occurring at that rate. This leads to errors because people develop expectations based on past experience rather than on the actual evidence at hand, and can come to expect an outcome even before seeing the evidence.

POSTbriefs POST-PB-0015

Authors: Sarah Bunn; Sophie Stammers

Topics: Crime, Research and innovation, Science

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The Parliamentary Office of Science and Technology produces independent, balanced and accessible briefings on public policy issues related to science and technology.