A question of science

A jury finds scientific testimony compelling enough to convict a British au pair of murder and a long stretch in prison. The judge disagrees, reducing the conviction to manslaughter and time served. Fifty doctors immediately denounce the judge’s decision, saying the defense’s medical evidence was inaccurate and unscientific.

By now, just about everyone knows the case of Louise Woodward and the tragic death of the baby in her care. But very few people know — can know — what to make of the highly contradictory scientific evidence produced at the trial. The case was a vivid example of the difficulties judges and juries face when trying to sort out the conflicting testimony of experts, a condition that will become more complicated as forensic knowledge grows.

Here is how baffled jurors can become when it comes to sorting out scientific evidence and questions of probability. It was not until last year, when tobacco companies were caught by their own documents, that courts began to find for plaintiffs in smoking cases. Until that time, the tobacco industry routinely put scientists on the stand to testify that there was no proof that smoking cigarettes led to health problems. And they never lost a case.

After many years of watching scientific testimony increasingly dominate, and sometimes confuse, trials, the Supreme Court in 1993 ruled in a case involving a morning-sickness drug that judges could aggressively screen out science that they found to be less than credible. One judge in Oregon did just that last year in a case related to illness caused by defective breast implants.

The au pair case dealt less with the recent high-profile DNA research now found at trials and more with equally difficult medical questions. Could the baby, jurors were asked, have suffered an extreme blow to the head that did not result in the baby’s death until some weeks later? Could the point of trauma “re-bleed”? The case was complicated by the defense tactic of ruling out the possibility of manslaughter as an option. But the true difficulty for jurors, or anyone, was to find a context in which to place expert accounts that flat out contradicted each other.

Jurors are not alone with this problem. The issue has concerned some judges enough that 35 of them serving in the federal courts met last year in Massachusetts to receive basic training from 20 scientists in such areas as odds ratios, phenotypes, gene banks and how DNA sequencing works. The training was organized by the Einstein Institute for Science, Health and the Courts, which is conducting a nationwide program to help judges understand genetics and molecular biology. The same level of background work in medical science would be necessary to understand some of the arguments made in the Massachusetts case.

But jurors under the current system never will be adequately prepared for the testimony they will hear at these difficult trials. The burden will increasingly fall to judges, as happened in the Massachusetts case, to take ever more responsibility in directing the outcome of a trial.