Skepticism is very much concerned with assessing the quality of evidence in support of a particular claim. But evidence means different things to different people. In the first of a two-part series, Jim Ring examines the legal profession’s view of the matter.

Our knowledge of the world is never certain, so what should count as evidence that a claim is true? For many people trained in science the legal system contains some very strange anomalies. Material can be accepted as evidence in court even though it would be given no weight at all in a scientific context.

People are sometimes imprisoned because juries are prepared to accept the unsupported word of witnesses. David Dougherty was in jail three years for raping a young neighbour. She said he had done so. No other evidence pointed to a conviction; tests on DNA were inconclusive. Later, better tests indicated that the girl had had sex with a man other than Dougherty.

Peter Ellis (the Christchurch crèche case) was jailed because some small children told the court he had done dreadful things. The same children told questioners that some women had done dreadful things, but they were not believed. They also told stories about Ellis that could not possibly be true and these were edited out of the story put to the jury.

In science experiments a control is a most important feature. Unfortunately controls are generally ruled inadmissible by judges. In the Ellis case there was an excellent control for the children’s credibility. How reliable were the children’s stories about the women, and how reliable were their stories about Satanism and black magic?

Eyewitness accounts are given great weight in our justice system; yet in the US it has been estimated that mistaken eyewitness evidence is responsible for about 80 per cent of the wrongful convictions that occur. The trial of Scott Watson (Marlborough Sounds New Year murders) was unusual in that eyewitness evidence was treated in a different manner. The prosecution held that part of the evidence of one of their own witnesses was in error. He had a distinct memory of a two-masted yacht; the prosecution argued that he must have seen one with a single mast. In future will eyewitness evidence be treated as less conclusive?

In New Zealand a cell-mate can claim to have received a confession of guilt from a person awaiting trial. That such an anecdote can be accepted as evidence in court would be beyond belief – except it happens!

It was reported last year in the UK that a judge instructed a jury not to bother about statistics and just to use their common sense (let us hope this report was inaccurate). But common sense is not a reliable guide in complex matters. Science and statistics often produce results that are quite counter-intuitive.

A conviction is only supposed to take place when evidence is beyond all reasonable doubt. In New Zealand people are sometimes convicted in spite of reasonable doubt.

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