Time and again on this blog, we’ve discussed the serious — sometimes fundamental — problems with many forensic science techniques.
We’ve mentioned the 2009 National Academy of Sciences and 2016 President’s Council of Advisors on Science and Technology reports that called many of these techniques into question. We’ve talked about the FBI’s admission that several forensic techniques lack sufficient scientific underpinning.
One of the ways that bad forensic science makes it into criminal trials is exaggeration by the analyst who performed the test. Far too often, analysts make misleading statistical claims about the certainty of the test. They convince juries that there is no question about the results when, in reality, human error makes its way into forensic tests all the time.
We recently discussed the results of the National Registry of Exonerations’ 2018 annual report. That report found that official misconduct was documented in almost 71% of all 151 exonerations last year.
A New York Times analysis has identified another leading cause of wrongful conviction that led to exoneration: exaggerated forensic evidence.
“A lot of the problem with forensic testimony is that the diagnosticity is overstated,” said the author of the report, a law professor at the Michigan State University College of Law. The evidence “gets dressed up with this scientific certainty that isn’t justified.”
Microscopic hair comparison is scientifically invalid
One of the techniques that the FBI admitted was scientifically invalid is microscopic hair comparison. Yet four years after the FBI’s admission, a man named Glenn Payne was convicted of child sexual abuse based on exaggerated hair comparison testimony.
An analyst testified that there was a 1 in 48 chance that a particular hair belonged to anyone other than Payne. He then testified that there was a 1 in 2,700 chance that a second hair matched someone other than the alleged victim.
Then the analyst did something strange. He multiplied 48 by 2,700 and concluded that there was only a 1 in 129,600 chance that the hairs had been discovered randomly. That calculation was improper, as the analyst later admitted.
The most he could scientifically say was that the first hair sample could have come from Payne and that the second hair sample could have come from the victim. That’s all that was warranted by the evidence.
It was later discovered that the child in question had not been abused at all.
We recommend reading the entire New York Times piece, which contains several other examples of how exaggerated forensic testimony resulted in false convictions.
It’s crucial for people to understand that real-world forensic evidence is not like CSI. Yet juries continue to accept forensic testimony as if it were unquestionable. It is not.
