THE NATURE OF THE FBI’S STATISTICAL ERRORS. What kind of statistical errors were made by the FBI forensic experts in testifying about human hairs? Hsu’s article tells how the witnesses exaggerated what their statistical evidence demonstrated. Hsu says: “FBI experts systematically testified to the near-certainty of “matches” of crime-scene hairs to defendants, backing their claims by citing incomplete or misleading statistics drawn from their case work.” This kind of problem is familiar—it is hard to explain precisely and clearly what statistics show and do not show, especially when results are stated in terms of probabilities.
But the underlying problem for the witnesses may have been that there was no knowledge base for their opinions. This sentence from Hsu’s article is very troubling: “In reality, there is no accepted research on how often hair from different people may appear the same.”