A cot death expert accused of misusing statistics has defended his evidence in the 1999 murder trial of Sally Clark.
Sir Roy has begun his defence in the GMC case
Professor Sir Roy Meadow is charged with professional misconduct over his evidence - Mrs Clark was jailed for killing two sons but cleared in 2003.
Sir Roy, who denies the charge, told the General Medical Council he used "ball park figures" in his evidence.
It comes as the Lancet journal said Sir Roy was a "scapegoat", and the GMC case should not have been brought.
In a statement, Mrs Clark said she was "incensed" by the Lancet's controversial intervention.
Sally Clark was convicted of murdering her two baby sons, Christopher and Harry.
Sir Roy told the GMC hearing that at a committal hearing for Mrs Clark, he was asked by defence counsel about the one in 1,000 figure for sudden infant death syndrome.
He said he did not remember where the figure had come from, but when it appeared in an article he had written in an eminent paediatric journal, no one had questioned it.
Sir Roy said it was a "reasonable ball park figure" for the incidence of sudden infant death syndrome for the population as a whole.
He said he had squared it to reach a figure of one child per million for two such deaths in the same family
He then calculated that because of Sally Clark's age and the family's relative affluence, the likelihood in their case was one in 73 million - the figure he used during her trial.
It 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.
'Not natural causes'
Sir Roy said he took the one in 73 million figure to be a "mean figure and there would be a degree of variation on either side".
But he told the GMC he did not see himself as an expert statistician.
"Although I have published quite a lot of papers, it's been mainly qualitative work rather than quantative work."
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
Asked what view he took of the risk of recurrence in 1999, Prof Meadow said it was "tiny, and for clinical purposes probably not meaningful".
He added that he had an interest in cases where there were a lot of deaths and knowledge of such details led him to take a particular interest in the recurrence rates of sudden infant death syndrome.
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.
He told the GMC he had concerns over the evidence he saw regarding both Harry and Christopher's deaths.
"I could not think of natural causes for the two deaths," he said.
Sir Roy began his defence on the same day the Lancet published its commentary on the case.
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."
But, in a statement, Mrs Clark and her husband Steve said: "We are surprised that the editor of a respected professional journal felt it appropriate to publish such partisan comments like this at such a time," they said.
"If the editor of a national newspaper had done the same in the middle of a criminal trial, on the day when the defence was due to open its case, then he might well have found himself in court for contempt for attempting to prejudice the outcome of the proceedings."
The case was adjourned until Monday morning when Prof Meadow will continue to give evidence.