The 2009 NRC-NAS report contained an assessment of hair analysis, says the manual, "observing that there are neither 'scientifically accepted [population] frequency' statistics for various hair characteristics nor 'uniform standards on the number of features which must agree before an examiner may declare a 'match'" The report concluded that "testimony linking microscopic hair analysis with particular defendants is highly unreliable," recommending DNA testing of the evidence where practical.
Hair analysis is better at excluding suspects than individuating them: E.g., they could tell if someone had blonde with straight hair vs. curly hair from an African American, whether hair had been dyed, etc.. But even the best estimates of the technique's accuracy say the possibility of a false match is 1 in 4,500 for scalp hair and 1 in 800 for pubic hair. Other proficiency studies, have found much higher "false positive" rates - sometimes above 12%. Even more damning, an examination of the first 137 DNA exonerations found that 38% included invalid hair comparison testimony, with most of the cases involving "invalid individualizing claims."
In the courtroom, prior to the US Supreme Court's Daubert opinion in 1993, "an overwhelming majority of courts accepted expert testimony that hair samples are microscopically indistinguishable." However, 1990 decision in North Carolina held it an error to admit testimony that"it would be improbable that these hairs would have originated from another individual." The court held that such testimony amounted "effectively to positive identification of the defendant."
The first, significant post-Daubert challenge to such evidence came in Williamson v. Reynolds out of Oklahoma in 1995, where a district court was "unsuccessful in its attempt to locate any indication that expert hair comparison testimony meets any of the requirements of Daubert." Before retrial, that particular defendant was exonerated by exculpatory DNA evidence.
The section of the manual on microscopic hair analysis concludes:
Post-Daubert, many cases have continued to admit testimony about microscopic hair analysis. In 1999, one state court judicially noticed the reliability of hair evidence, implicitly finding this evidence to be not only admissible but also based on a technique of indisputable validity. In contrast, a Missouri court reasoned that, "without the benefit of population frequency data, an expert overreached in opining to "a reasonable degree of certainty that the unidentified hairs were in fact from" the defendant. The NRC report commented that there appears to be growing judicial support for the view that "testimony linking microscopic hair analysis with particular defendants is highly unreliable.RELATED: Go here to read the manual online or purchase a hardcopy. See also: Judges cautioned against reliance on overstated ballistics testimony.