Standards For DNA Identification Practice
In essence, DNA evidence is rapidly becoming, in principle, an irrefutable proof of identification. But of course, nothing is ever so simple. Scientists are a demanding lot, a skeptical lot, a rigorous lot. It's not enough to say it's okay in principle - it must be okay in practice as well. And although everyone agrees that this is a spectacular technology, controversies have erupted in the scientific community from time to time over whether it's really being done right. Fights erupt over DNA fingerprinting because it's such an important technology.
What have these fights been about? They have not been about how to do it in principle. They have been about how to do it in practice, and how well-regulated the practice is. For example, DNA fingerprints should look like bar codes. Here is a not-very-good example of a DNA fingerprint, which was used in a criminal case in New York. It's one I know well, because it was one where I was asked to serve as an expert witness, which is how, from my medical genetics background, I got deeply involved in this.
It was an interesting case, because it showed what scientists can do when they put their heads together. Halfway through this case, when all the evidence was being considered, all the scientists who had testified as witnesses for the prosecution, and all the scientists who had testified for the defense, met outside the courtroom without the lawyers present and talked about the evidence. And at the end of the day we agreed the evidence was terrible, and we went back to court with a joint statement for the witnesses on both sides, saying the evidence was no good. It was the first case in which DNA fingerprinting was actually thrown out because of the way it was practiced. It was also an example, I think, to the legal community, that scientists are not necessarily hired guns to say whatever you tell them to say.
The other controversy that has arisen is about how to interpret a match. What frequency should you put on it? How rare is a pattern? How odd is a match? And for this, the controversy is a technical one and a complex one, but it has to do with the fact that the frequency of the different DNA patterns of different genes vary across the population. This is actually a blood group frequency distribution. Similar things are known for other types of DNA differences. And so there has been active controversy about exactly what weight we should put on samples. Are the odds being quoted one hundred-fold too high? Are they exactly right? Maybe they're one thousand-fold too high. Scientists are arguing actively about this.
There is a good mechanism in the scientific community for focusing on such arguments. It is the National Research Council Committee from the National Academy of Sciences. For my own sins in that New York case, I served on this Committee for a period of three years, which finally culminated in the production, after a very, very long gestation, of an NRC report called, "DNA Technology in Forensic Science."
The really important thing the committee has done is calling for defined standards for laboratory work. For new standards of statistical calculations. And most importantly to my mind, it called for a mandatory proficiency test - that the laboratories that are doing this work should be subjected regularly to blind proficiency testing, to insure that they did the work well on a regular basis. It is in some sense appalling that there are no mandatory standards for something as important as forensic testing. There are higher standards, indeed for the laboratory practices of someone who will diagnose strep throat than for the laboratory practice of someone who will create a DNA fingerprint that could be used to send someone to Death Row.
  
|
Winding Your Way Through DNA Resource Book Index
