Opposing experts proclaim end of DNA evidence debate.

"The DNA fingerprinting wars are over." With these words, two noted experts who have battled over the validity of forensic DNA evidence for years recently declared an end to the nationwide dispute. But courts are still wrestling with whether this evidence should be admitted in criminal trials and, if so, what weight it should be given. The most prominent example is the case of O.J. Simpson, charged with the murders of his ex-wife and her friend.

Dr. Eric S. Lander, a molecular biologist at the Massachusetts Institute of Technology, previously opposed the use of DNA evidence in criminal court. Dr. Bruce Budowle, a chief scientist for the Federal Bureau of Investigation (FBI), argued in its favor. In a recent issue of an influential science journal, they wrote that they could see "no remaining problem that should prevent the full use of DNA evidence in any court." (Eric S. Lander & Bruce Budowle, DNA Fingerprinting Dispute Laid to Rest, NATURE, Oct. 27, 1994, at 735.)

The article reconciles their positions on two key problems: how to account for the error rate of laboratory personnel and how to calculate the probability that another person's DNA "profile" is the same as the source of the evidence--in other words, how to calculate the rarity of the profile.

Estimates of a rate of 1 in billions for a random match have been calculated. Critics of DNA evidence say that the size of these numbers and the aura of certitude that attaches to science give the DNA evidence too much weight in jurors' minds.

The techniques for making DNA profiles date back less than a decade and are still being developed. Initially, the laboratories doing the tests and providing the statistics were not certified and did not account for operator error in their figures. DNA lab certification is now available but is not yet required for DNA evidence to be admissible.

Criminal defense lawyers at first did not know how to handle DNA evidence. After becoming familiar with it, they pointed out that a laboratory error rate of 1 in 100 would make a calculated random match probability rate of 1 in 1 billion meaningless. (See William C. Thompson, DNA Evidence in Criminal Law: New Developments, TRIAL, Aug. 1994, at 34.)

Match rate statistics are based on the assumption that the labs are testing rare DNA segments that are inherited separately. The figures are found by multiplying together the incidence rates at which the various segments are found in a population. The more segments are used and the rarer they are believed to be, the lower the probability that the DNA could have come from someone other than the match candidate.

Another possible problem with the figures is lack of representativeness of the population databases. Critics pointed out that some of the DNA segments used in testing are found more often in some ethnic groups. Others said that the sample populations used by the labs to establish how often the segments occur were small and selected arbitrarily.

To overcome these criticisms, the National Research Council (NRC) proposed two years ago that in calculating the likelihood of a random match, litigants should use the "ceiling principle": use only the highest rate of incidence found in any group for each segment. (National Research Council, DNA Technology in Forensic Science (1992).) At the FBI's request, the NRC is revising its report in light of the criticisms it received. But even before the revision, using the ceiling principle produces impressively low random match probability figures. Lander and Budowle agreed that this conservative procedure is desirable.

Many other experts reject this rationale and are less hopeful that the conflict has been laid to rest. Dr. Jerry Coyne, a population geneticist at the University of Chicago who opposes use of the evidence in criminal cases, told a reporter, "There's plenty of controversy in the field.... [This] was carefully calculated to come out right before the DNA hearings for the Simpson case. The only motive I can see is to influence the judge." (Gina Kolata, Two Chief Rivals in the Battle Over DNA Evidence Now Agree on Its Use, N.Y. Times, Oct. 27, 1994, at B14.)