22 January 2006

The science of the expert witness

There are many court cases that rely on the evidence of an expert, whether they are forensic, medical, scientific, financial, or some other type of specialist. Inevitably this means both prosecution and defence will need to have their own set of experts, who are then encouraged to throw counter arguments at each other. The jury listen to both teams of experts, and then, with their layman viewpoint, they must decide who is telling the truth or making the best arguments. You do not have to look hard to see there are good possibilities in this situation for misleading a non-expert jury, and average juries do not include many experts - they may in fact consist of people such as housewives, shop assistants or bus drivers.

Having been extremely concerned at the poor quality of expert evidence used by the prosecution at my trial in 1993, I was very interested to read a letter that appeared in the New Scientist magazine, which confirmed my worst fears that confusion over expert evidence was not an uncommon problem. The letter can be read on the New Scientist website
here, but for convenience I print it below:

29 November 1997
New Scientist

Death of science

I read with interest your editorial “Death of an expert witness” (8 November, p 3). As one of the defence’s expert witnesses (I am a neuropathologist) in the Louise Woodward trial, when the verdict “guilty of second degree murder” came in, I viewed the real verdict as “death”. Not the death of Woodward, who as it turned out, was saved by judge Zobel’s intercession, but a death of logic and science.

During the last phase of the trial, virtually every television reporter, and many of the “former” prosecutors who had been retained as commentators, usually prefaced their comments with statements to the effect that “they didn’t know science, and therefore could not interpret the evidence”. More shocking still, they would then go on to imply that this same level of ignorance extended to the jury and that because various experts had taken opposing positions, the scientific testimony should be disregarded as irrelevant and the outcome judged on the demeanour and testimony of the defendant. To my horror, when the verdict was reported, it appears that the jury had done exactly that.

The prosecution’s expert testimony was heavily laced with beliefs and dogma - for example, retinal haemorrhages mean shaking, infant head injuries rarely, if ever, have latencies, and so on. A jury properly briefed on the science would have recognised that.

Perhaps what is being said here is not so much that we should be excused for our lack of detailed scientific knowledge, but that we should also be excused for not knowing how to think critically and evaluate information that comes to us. If this is the case, and I suspect that it is, then we are all in very deep trouble. Our educational institutions must have, indeed, failed utterly.

I don’t think committees can replace individual experts’ opinion, but open forums for discussion can provide a context within which dissident opinion can be weighed, and “junk” science and dogma exposed. How the legal system can effectively utilise expert opinion is a thorny problem. It is high time that judicial conferences, lawyers’ organisations, advocacy groups, and other interested parties visit the broad issues raised with the Woodward case, and try to find a better way to elicit solid opinion and employ it in the delivery of justice.

Jan E. Leestma
The Chicago Institute of Neurosurgery and Neuroresearch, Chicago

New Scientist article

I do not like censorship - Full Sutton prison prevented me from posting my reply to New Scientist - and I demanded the right to say what I wished to say. Eventually, the MoD agreed that my letter did not infringe the Official Secrets Act, and I was allowed to send it, although after more than 2 years my letter had no chance of being published as a reply to Mr Leestma’s letter. For the record I can now publish my letter below, and I hope you will see that it was relevant to Mr Leestma’s original points:

I agree with Jan E. Leestma's views on expert testimony (Letters, 29 November, p 61), but I blame the adversarial justice system for prostituting science - experts are used as weapons against each other, rather than to determine Truth.

I was convicted under Britain's Official Secrets Act, for allegedly leaking military secrets, after 20 prosecution experts said the exhibits were "sensitive". Nevertheless, my one defence expert proved the exhibits were either in the public domain or innocuous.

One "restricted" document, the only classified document in my case, became the key scientific issue. The document was a SAW filter specification - its actual use was not identified - but my expert recognised, from a sales catalogue, that it was a commercial product.

A prosecution witness, Dr Meirion Francis Lewis - the only witness to testify on the document - claimed he could identify its use on Britain's ALARM missile, and he said it would enable an enemy to jam the missile. As an electronics engineer myself, I believe Dr Lewis's deductions are impossible, and that his evidence was wrong.

Dr Lewis said he was told on the telephone that the document was used on ALARM, and he appealed to patriotism by saying fear of ALARM caused Iraq to switch off its radar systems during the Gulf War.

Although Dr Lewis admitted he was not an expert in missile technology, nor in jamming, the prosecution withheld his evidence for 14 months until my trial. No ALARM expert was used by the prosecution. The judge found these anomalies acceptable.

Due to the nature of my case, the defence could not find an expert to oppose Dr Lewis's evidence. However, the accuracy of his evidence remains obscure, as the Security Commission's report on my case (HMSO, Cm2930, July 1995) states: 'at the time the document was created it was not specifically linked to a particular weapons system' (Annex A.5).

If Justice is based on Truth, then scientists, and not lawyers, should determine the validity of scientific evidence. Juries should not be asked to decide which expert is honest; nor should a Counsel win cases by relying on the scientific ignorance of jurors.

I should add that, since giving his evidence at my trial, Meirion Francis Lewis has been awarded the CBE and is now referred to as a Professor.

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