OXFORDSHIRE’S hospital authority bosses say it was wrongly named as one of England’s worst for “unexpected” deaths because of a calculation error.

Oxford University Hospitals NHS Trust said it over-reported the number of “unintended or unexpected” deaths because of ambiguous Government guidance.

Patient safety incident reports – published online – recorded 29 deaths from April to September last year, the highest of 30 similar authorities classed as teaching trusts.

Most recent figures – for September to March – saw the number of reported deaths drop to six. Some 17 trusts reported fewer deaths, with London’s Barts Health NHS Trust recording the highest, 26. The figures are provided by trusts to NHS England, which publishes them online.

NHS England declined to add to the statement.

OUHT medical director Professor Edward Baker said the figures “were based on a calculation error, and we do not believe that future figures will look like this”.

He said NHS guidance “was ambiguous” adding: “Initially our calculations were out of step with the way other trusts were reporting it.”

He said: “When we reviewed the grading of incidents using the same criteria as other trusts, the figure was reduced to six.”

This was because the trust used a new data collection process called Datix from April to September 2012 which assesses the contribution trusts may have made to a patient’s death.

He said: “The figure that the trust originally reported included deaths that should not have been included.

“The trust did not realise this until after the date for submitting the figures had passed.”

For 2010/11 there were 14 trust deaths reported and four in 2011/12.

Prof Baker said: “We seek to learn any lessons that can be learned from every death in the trust.”

Oxford East Labour MP Andrew Smith said: “It is a real concern that there seem to have been calculation errors in something as important as this, and simply not good enough if the national guidance was ambiguous.

“I shall find out more about this and take it up with the Secretary of State for Health.”

Larry Sanders, chairman of Healthwatch, the county’s official health and social care watchdog, said the data should be an important guide to patient safety at the trust.

He said: “These patient safety reports are one of the very important clues as to what is happening on the wards.

“Healthwatch Oxfordshire will be having regular discussions with the trust and we will want them to explain what they are learning from these pointers and what they are doing about the worrying ones.”

The issues comes after the OUHT this month rejected NHS England statistics which put it as one of the worst in the country for cancelling routine operations. The trust said some procedures could have been counted twice.