Researchers outside the F.B.I. posit that the Journal of Forensic Sciences article also failed to show that jeans bar codes were a reliable method of identification. The major problem, they say, was that the article did not include an objective statistical model of how likely it was for the method to make mistakes — to gauge the possibility that two different pairs of jeans might look the same because of manufacturing similarities or just by coincidence, for instance. Instead the study leaned on the analyst’s judgment of markings on jeans.

Dr. Vorder Bruegge pointed this out himself in the study: “It should be remembered that in this and other cases, the overall significance of wear marks is not necessarily based on a quantitative assessment, but on a qualitative assessment.”

During the trial of Mr. Barbee, Dr. Vorder Bruegge demonstrated the accuracy of the technique by explaining that one pair of jeans seized from Mr. Barbee matched the pair worn by the bank robber, while 34 other pairs of jeans offered up by the defense did not. But outside researchers say that method does not substitute for having a statistical model describing the method’s accuracy.

In fact, at four points in the article, Dr. Vorder Bruegge noted that the technique had yet to be statistically validated. “Although a validation study has yet to be performed to test the theory that all denim trouser bar code seam patterns are unique,” he wrote, “it has been observed in numerous examinations that it is possible to distinguish pairs of jeans from one another based solely on differences in the patterns along the seams.”

No such validation study has been published since then. The F.B.I. declined to answer questions about the bureau’s use of jeans bar codes or about Dr. Vorder Bruegge’s research. Independent researchers say that with many other kinds of pattern analysis, as with jeans bar codes, prosecution witnesses rely too much on subjective judgments rather than rigorous statistics.

“Forensic scientists will say, ‘Yeah, I’m sure, based on my 20 years of experience, that these prints were made by that same finger,’” said Anil Jain, a computer scientist who studies pattern recognition and biometrics. “They say that’s a subjective decision. We want to get away from that.” F.B.I. investigators sometimes present the methods in court as being near-infallible, often citing levels of accuracy that researchers find implausible.

In a 2003 case, Dr. Vorder Bruegge claimed that the plaid shirt worn by a bank robber and captured by a security camera made a definitive match with one seized from the home of a suspect. He testified that only one in 650 billion shirts would match so well — a claim that “makes about as much sense as the statement two plus two equals five,” Karen Kafadar, a statistician at the University of Virginia, told ProPublica.