Don’t Fall for the CSI Effect

In crime shows, teams of superhero cops are often shown relying heavily on forensic evidence when prosecuting criminals, but how reliable is forensic science in reality?

Crime TV shows like NCIS, Sherlock, and Law and Order have captivated generations of TV viewers. In the spring of 2017, over 96 million in the U.S. said they typically watched mystery/suspense/crime programs on TV. [1] In many popular crime dramas, police officers and private investigators almost never fail to find the true criminal, and forensic evidence is often presented as undeniable proof linking the culprit to the crime. Forensic analysts always succeed in finding a match between the evidence found on the crime scene and the DNA, fingerprint, hair, or even teeth (when looking at bite marks) of the accused, and coroners are able to determine the precise cause and time of death. All conclusions are reached almost immediately in the forensic lab. The reality of criminal investigations, however, is far from what is depicted in these TV shows. 

It is because of the motivation of TV producers to make the story entertaining and fast-paced that many experts express concerns about how the public is affected by exposure to crime shows and other forms of media that depict forensic science as an infallible source of incriminating evidence. They’ve dubbed it the “CSI Effect” after the popular TV show CSI: Crime Scene Investigation, claiming that the exaggerated portrayal of forensic evidence of crime television impacts public perception particularly in the criminal justice system where jurors can be influenced to have unrealistic expectations of forensic science in criminal trials. [2] According to the CSI Effect, consumption of crime media can ultimately affect jurors’ decisions in the conviction or acquittal process. [3]

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A Pew Research Center survey shows that a majority of Americans believe that shows and movies about criminal investigations help or do no harm to their understanding of science. Some experts beg to differ.

Although the CSI Effect is theoretically plausible, empirical research on the phenomenon offers conflicting evidence. [3] While some studies claim that the CSI Effect doesn’t really exist, others have demonstrated that a “pro-defense bias” in which jurors are less likely to convict in the absence of forensic evidence. [4] [5] Several studies examining the CSI Effect have also found proof of advantages for the prosecution when forensic evidence is present such as the bolstering of the credibility of forensic experts and the evidence presented in their testimony. [6]

In criminal cases, the standard that must be met by the prosecution is proof beyond a reasonable doubt that the defendant committed the crime, and it is the highest burden of proof that must be met in any trial in the U.S. justice system. Although forensic evidence does not inherently carry more weight than other types of evidence, the overstatement of forensic evidence in various forms of media has the potential to misguide the jury to believe that forensic evidence eliminates any reasonable doubt. It also doesn’t help that jurors can be further deceived by the misleading (or sometimes outright false) testimony of forensic specialists in court.

A report by a Presidential Science Council found that expert witnesses frequently exaggerate the value of their evidence; for instance, some examiners have testified that their conclusions are “100 percent certain” and that their conclusions have an “essentially zero” error rate. [7] Numerous reviews, however, have revealed that such statements are not scientifically defensible because no laboratory test has a zero error rate. [7] A review of expert testimony regarding microscopic hair analysis by the Department of Justice and the Federal Bureau of Intelligence in 2012 also found that FBI examiners provided scientifically invalid testimony in more than 90 percent of cases where examiner provided testimony was used as incriminating evidence. [8]


A political cartoon from the University of Texas at Tyler depicting an extreme case of the CSI Effect where a juror asks for incriminating DNA evidence even after the defendant pleads guilty.

One of the key roots of this problem is that the fact that in most criminal cases, forensic laboratories have close ties to the prosecution, which seriously undermines the objectivity of the conclusions made because forensic experts are subject to “subtle cognitive bias and overt pressure from the police.” [7]

There seems to be a great necessity for reform not only in how jurors are instructed to accept different types of forensic evidence but also in how expert witnesses testify and reach their conclusions in laboratories.


– Kristin Kim (’20)




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