A child death expert accused of misusing statistics in a murder trial has described the "ordeal" of giving evidence in criminal cases.
Sir Roy has begun his defence in the GMC case
Professor Sir Roy Meadow is accused of professional misconduct over evidence he gave in the 1999 trial of Sally Clark. She was jailed but later freed.
Sir Roy, who denies the charge, told the General Medical Council giving evidence was a "legal jousting match".
It comes as the Lancet journal said the GMC case should not have been brought.
The leading medical journal said Sir Roy, who could be struck off if found guilty, had become a scapegoat and called for a royal commission to be set up to look into all the issues surrounding the case.
During the Clark trial, Sir Roy said the probability of two natural unexplained cot deaths in the family was 73 million to one.
Sally Clark: Served three years after being wrongly convicted of killing her two sons
Angela Cannings: Served 18 months after being wrongly convicted of killing her two sons
Donna Anthony: Served six years after being wrongly convicted of killing her son and daughter
Trupti Patel: Cleared of killing three of her children
The figure was later disputed by the Royal Statistical Society and other experts have said that once genetic and environmental factors are taken into consideration, the odds are closer to 200 to one.
Mrs Clark was eventually freed in 2003, after an appeal overturned her conviction.
Sir Roy also gave evidence as an expert witness in the trials of two other women, Angela Cannings and Donna Anthony, who were both freed on appeal after being convicted of murdering their children.
In his first day of his defence at the GMC he said giving evidence in criminal cases was an ordeal for which he had received no formal guidelines.
"Giving evidence in court is a great ordeal I think for anybody and anyone who gives evidence in court is very nervous, however many times you have been there."
He said that like an exam, it was possible to come out of court furious for not expressing what one had said in a better way.
Sir Roy said a family court everything is geared towards the best interests of the child, not unlike medicine.
Reports are not censored, and the whole thing goes to the judge, he added.
But he said in criminal courts, the jurors must go on the results of a "jousting match between the advocates."
Sir Roy also described research to the GMC which found that the sudden death of a child was a factor in mother's fabricating illness in a subsequent child - a condition known as Munchausen's Syndrome by Proxy.
He said evidence suggested that a significant proportion of children who had died suddenly may have been smothered by one of their parents, but added when he first suggested it he faced strong resistance.
But added: "There was disbelief from social workers that this sort of thing could happen, either severe fabricated illness or smothering. It was a very difficult period."
The Lancet said the case was a legal and not a medical one.
Editor Dr Richard Horton said Sir Roy had been a "lightning rod of blame" for the wrongful conviction of Mrs Clark.
"This misconceived pursuit of one man is wrong and threatens the effective delivery of child protection services in Britain."
He said the activities of the police, pathologists, lawyers and other experts involved in investigating suspicious death need to be considered together and says a royal commission should look at the issues.