Lucy Letby unit baby death increase ‘not extreme’, inquiry hears

Sir David pointed out that no statistical monitoring system could reveal the reason or reasons why something had happened.

A classic example of a statistical outlier occurred at Bristol Royal Infirmary in the 1980s and 1990s, he said, which revealed failings in paediatric heart surgery.

Sir David, who headed a team of statisticians for the subsequent public inquiry, said there was “clear water” between Bristol and 11 other centres.

This was not the case for the Countess of Chester Hospital’s neonatal unit, he said.

Sir David said its mortality rate in 2015 and 2016 was only 10% higher than the average for neonatal units with similar birth rates.

He said the Countess of Chester was highest in its tier of centres, but “only just”.

“One would not call that an outlier,” he said.

Letby is serving 15 whole-life sentences after she was convicted at Manchester Crown Court of murdering seven infants and attempting to murder seven others, with two attempts on one of her victims.

The public inquiry, chaired by Lady Justice Thirlwall, is hearing its final week of evidence at Liverpool Town Hall.

Her findings are expected to be published in the autumn.

Additional reporting by the Press Association.