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Monday, 21 February, 2000, 08:11 GMT
Doctors' evidence in court 'biased'

Expert witnesses in court Expert witnesses are hindsight biased says report

Doctors called as expert witnesses in medical negligence cases are biased by hindsight, it has been claimed.

They have an advantage over the doctor on trial because they already know the outcome of a patient's condition.

Psychologist Professor Al Arkes, of Ohio University, says although it makes for a convincing testimony, it is not always an accurate one.

And hindsight bias can predispose a jury in a medical malpractice suit to a guilty verdict, he says.

It's important to try to get people to say what they would have done without knowing how it turned out
Professor Al Arkes
And he believes the court system should be changed so that expert witnesses would give their opinion without knowing what the original outcome was.

Professor Arkes said: "It's important to try to get people to say what they would have done without knowing how it turned out."

Sir Christopher Paine, a former governor of the Expert Witness Institute in the UK, said every expert witness in a court case has the advantage of hindsight.

He said: "All expert witnesses have the benefit of hindsight.

"But I think they play an important role in court cases.

"I believe juries know expert witnesses have hindsight benefit and take this into account when considering verdicts."

Hindsight knowledge

Professor Arkes carried out a study which showed how doctors with hindsight knowledge reached different prognoses than those acting with foresight.

Teaching hospitals often require physicians and students to participate in clinicopathologic conferences - where one person presents a medical case, offers a diagnosis and awaits the actual cause of death given by a pathologist.

However a survey, carried out by Professor Arkes and Case Western University researcher Professor Neal Dawson found these forums were ineffective due to physician over-confidence attributable to hindsight bias.

A total of 160 doctors and medical students in Cleveland were involved in a study to look at the outcome of prognoses.

I believe juries know expert witnesses have hindsight benefit and take this into account when considering verdicts
Sir Christopher Paine
Half, called the foresight group, were asked to complete a questionnaire after the case was presented but before the cause of death was revealed. There were five possible diagnoses.

The other half, the hindsight group, was asked to fill out the same questionnaire after the pathologist revealed the actual diagnosis.

The results showed the foresight group were less likely to select the correct diagnosis while the hindsight group were more likely to select the correct one.

Lost opportunity

Professor Arkes said: "Rather than learning as much as they could, the physicians in the hindsight group felt they knew the right answer all along.

"They lost a wonderful educational opportunity."

"Removing hindsight bias from a courtroom is a more difficult task, but one the courts should attempt if a fair verdict is the desired outcome."

Professors Arkes and Dawson presented their findings at the American Association for the Advancement of Science meeting in Washington.

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