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Expert Report Urges Changes to Forensic Analysis in Courtrooms

by Dale Chappell

Instead of subjective personal experiences, a new report by experts urges prosecutors and forensic experts to rely more on hard data and statistics to back evidence in a criminal case. A defendant’s life might rely on it. Literally. 

“If you’re overstating or understating the value of the evidence, there are several harms that can occur,” said Hal Stern, vice chairman of the American Statistical Association (“ASA”) Advisory Committee on Forensic Science. Concerns about the use of forensic evidence, such as shoe prints, bite marks, fingerprints, and hairs and fibers, which have contributed to numerous documented wrongful convictions, prompted the ASA to issue a report pushing for more reliance on stats and data, rather than assumptions based on past practice. 

“Forensic practitioners are well-meaning,” Stern said. But, “they’re trying to assess the relevance or value of that evidence for prosecuting a crime.” 

Matt Redle, a former prosecutor who served on the National Commission on Forensic Science, said, ‘‘We really didn’t know a lot about this, and we assumed the forensic evidence we were working with was true and correct.” However, evidence assessed and weighed against stats and data, like DNA evidence, “was the eye-opener for prosecutors” and the legal system overall, he said. 

The idea in the report is to get everyone involved, from crime-scene techs to prosecutors, to use data to “quantify the value of evidence being presented in criminal cases and thereby increase our confidence in the judicial system,” ASA president Karen Kafadar said. The report encourages all involved to follow “reliable and valid” processes in presenting evidence. 

Peter Newfeld, co-founder of the Innocence Project, said, “the ASA statement being adopted by the entire organization is extremely important because the ASA has an extraordinary reputation and a very large membership.”

He recalled that “we have plenty of first-hand encounters where forensic examiners relied on their subjective impressions and personal experience instead of statistical data to explain the value of the evidence.”

So, “as a consequence, there were serious miscarriages of justice, where factually innocent people lost decades of their lives and some of them were sentenced to death.” 

An example provided by the ASA explains the idea in practice: Glass fragments found to have similar trace element composition could come from a common origin but would need to be demonstrated with a database showing how common that glass is — and then what the findings mean to the criminal charges. This “requires knowledge of how common or rare the association is, based on empirical data linked to the case at hand,” according to the report. 

Just like with DNA database information, forensic experts could rely on a database with verifiable information, rather than their so-called “expert opinion.” And they should, the ASA contends. 

“Credibility in the system is the greatest asset prosecutors have,” Redle said. “There’s damage we do to the system and credibility in our rule of law if we’re hiding the ball from our juries about what the limitations [of forensic evidence] are. It’s far better to be open and upfront and recognize the limitations.”  



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