Did I read this correctly? Fifteen percent -- one out of every six or seven -- of the men and women in prison are innocent? That is almost four times the 4% rate estimated in Gross et al. (2013). But that study, the leading one in the field, was limited to defendants with death sentences. Their cases would have been scrutinized especially carefully, so the 4% figure is probably on the low side. Maybe 15% for the broader prison population is realistic.
But wait. Forensic Magazine was not referring to the entire prison population, but only to those cases that went to trial. And within that group, 15% is the figure for defendants for whom "DNA was an element in their trial[s]." Because almost no defendants introduce DNA evidence at trial, these must be cases in which the prosecution has linked the defendant to the crime by DNA testing and the state "misused DNA ... techniques." Can it be that 15% of inmates convicted because of DNA tests are falsely convicted? That is an intolerable error rate for what is supposed to be the gold standard in forensic science. Is it time to halt DNA testing until we can find out why it generates so much "scientifically invalid testimony"?
Or are the editors of Forensic Magazine seeking sensational news rather than reading what they are reporting? Let's look at the "recent estimates." To get to them requires a few steps backwards. Forensic Magazine lists the National Institute of Justice (NIJ) -- a part of the U.S. Department of Justice -- as the source of its story. NIJ funded the Rand Corporation to do a study on improving expert performance in computing a posterior probability (which is not what forensic experts routinely do). Rand investigated two questions: "Is bias reduced when experts do not know whether the prosecution or defense is the hiring party?," and "Is bias reduced by expert consensus feedback, wherein expertise is culled from multiple sources and those sources examine the majority view to move toward a group consensus?"
The summary at the start of the Rand research report begins with the very two sentences that Forensic Magazine broadcast. The researchers gave no references to indicate where these "recent estimates" came from, but page one of the report supplies an apparent answer. It reads as follows:
This passage reveals that Rand simply misrepresented the "recent estimates" in the first instance. Roman et al. (2012) is an NIJ-funded study from the Urban Institute that involved no cases of wrongful convictions because of misused DNA evidence. Instead, that study "analyzed the results of new DNA testing of old physical evidence from 634 sexual assault and homicide cases that took place in Virginia between 1973 and 1987." In other words, it looked at postconviction exonerations in cases in which the trials took place before DNA evidence was even available. This study of wrongful convictions for reasons other than faulty DNA evidence "found that in five percent of homicide and sexual assault cases DNA testing eliminated the convicted offender as the source of incriminating physical evidence. When sexual assault convictions were isolated, DNA testing eliminated between 8 and 15 percent of convicted offenders and supported exoneration."
Are there any cases of false convictions caused by DNA evidence? Almost certainly. Does the rate of such convictions approach 15%? Neither Forensic Magazine, NIJ, nor the Rand Corporation offers any reason to believe it.