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Juror Bias Often Triggered by Severity of Crime Charged

by Ed Lyon

Duke University’s Institute of Brain Sciences recently partnered with the National Institutes of Health and National Science Foundation to study the effect of crime severity on jurors’ psyches prior to hearing evidence. The study’s full results were published in the October 29, 2018, issue of Nature Human Behavior.

Six hundred lay persons were assessed online via computer based on their reading of 33 types of cases, from bootlegging to mass murder. They were told to rate the strength of each case on a 0-to-100 scale. Researchers found that the more serious the crime, the greater the likelihood of a finding of guilt.

The same study was repeated with a combination of law students, defense and prosecuting attorneys, and judges. The in-built bias phenomenon diminished with this group who were trained by education and practice to pass judgment on individual cases according to the evidence present in court rather than a crime by its description.

Part of the study evaluated how the weight of different types of evidence affected participants. DNA and physical evidence, such as fingerprints, added around 30 points to a mock juror’s view of a case. Lead study author John Pearson, referring to the popular television crime drama, stated this was the “CSI effect” where people expect the kind of dedicated technicians with sterile and well-equipped laboratories they see on television to be used in the real world.

In contrast to the earlier comparison between lay participants and legal professionals, judges and lawyers upgraded their beliefs in a case by 40 points in the face of DNA and physical evidence. Senior study author Pate Skene stated, “There’s a certain irony in the fact that the better a scientific method is, the harder it is to remember that it’s sometimes wrong.” He added, “While the study shows that mock jurors need less evidence to convict serious crimes, they should actually require more [evidence].”

Follow-up studies using MRIs to evaluate how participants’ brains activate during the evidentiary evaluation process are being planned. Understanding of how inner emotional and moral struggles influence a person’s decisions when considering, for example, the risk of freeing a murderer versus imprisoning an innocent defendant is one of researchers’ goals. 



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