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Fingerprint Identification: (This article was obtained from the Internet website “The Why Files” at http://whyfiles.news.wisc.edu/index.html. This site is funded by the National Institute for Scientific Education.) It seemed strange at one point, but we've grown to accept the idea that each person's fingerprints are unique. Today, “fingerprint” defines the perfect identification technique, and when we use DNA to conclusively identify someone, we call the process “DNA fingerprinting.” Accepted is one thing, but proven beyond a reasonable --— or at least scientific --— doubt, is another. David Stoney, a forensic chemist who directs the McCrone Research Institute in Chicago, wants to know “how much science is there to back up fingerprint identification?” Stoney, who wrote his doctoral dissertation on the statistics of fingerprint identification, admits that those little ridges and whorls can be pretty convincing: “There are some prints that are big enough, and good enough quality, that it would be irrational to dispute them.” But when an identification is based on partial or degraded prints, “Where do you get to the point that there's not enough information?” Is half a print enough to finger (pun intended) somebody for murder? One quarter? Even if each print is unique, can people share identical half prints? Quarter prints? The goal is to maintain public confidence in fingerprint identification, he adds. “They have said that as a profession they have an obligation to show that they are 100 percent certain all the time, and therefore we'll never show fingerprints that are less than 100 percent sure. Fingerprint examiners sometimes say it's unethical behavior to give a qualified identification.” Still, fingerprints can be used to open doors, as you'll see in the slightly annoying code behind this button. If fingerprint evidence were introduced today, Stoney says, “it would be very difficult to prove it statistically,” to anything like the standard DNA identification has had to meet. The main problem, he says, is mathematically quantifying the endless variations of shape. And since the experts cannot quantify their opinions, they must rely on their experience to render an expert opinion: “After examining thousands of fingerprints, I give you this opinion.” Ironically, he adds, even though fingerprinting is less quantifiable, and thus less scientific, than DNA identification, it can be more convincing. For one thing, it's part of daily reality: “You can look at your fingers, and there's all this variation, and you can look at the expert's picture, and compare the unique points.” And that makes it more comprehensible to jurors. For another, all that scientific accuracy may backfire against DNA testimony. “A gigantic number, like one chance in 50 billion that a DNA match is due to chance alone, may make [a juror] think more, question more, than an expert's assertion” that a fingerprint is unique. “The juror may wonder, how can you say this, you might be wrong. A number like one in 50 billion is foreign to a lay person's experience.” Still, Stoney says, he'd be happy to be convicted on either kind of evidence --— DNA fingerprinting or the kind that's literally “at your fingertips,” as long as foul play could be ruled out --— on the part of the expert witness. So what's new in DNA fingerprinting, anyway? (Editor--—While surfing the internet early one morning several months ago, this article caught my eye and caused me to ponder the question “If fingerprint evidence were to be introduced today for the first time, would we be prepared to support its scientific foundation?” While Stoney was addressing the “opinions” (or conclusions as Tom Jones aptly argues on page 9) of the examination, and not the foundational tenets, his article's title and the suggestion of challenges which could occur with today's climate, prompted my writing the paper on the following pages.)
This article was reprinted in “THE PRINT” |