Incorrect statistical reasoning in Guyll et al. leads to biased claims about strength of forensic evidence

Guyll et al. (1) make an error in statistical reasoning that could lead judges and jurors in criminal trials to grossly misinterpret forensic evidence. Their error leads to highly inflated claims about the probability that a cartridge case from a crime scene was fired from a reference firearm, typically a firearm found in the possession of a defendant. These claims are being presented in at least one ongoing homicide case (2). We wrote a paper to address this error, summarized here. Some text below is excerpted from (3).