A top statistician has thrown a bucket of cold water on the stab murder media hysteria which has gripped the UK - and especially London - during the past year.

Professor David Spiegelhalter, Winton Professor of the Public Understanding of Risk at the University of Cambridge, has just published a study on the subject in Significance - the magazine of the Royal Statistical Society.

He has harsh words for comments like that of BBC correspondent Andy Tighe on July 10 last year, following four knife killings that day. Tighe said: "To have four fatal stabbings in one day could be a statistical freak."

Au contraire, says the prof. It was a normal event, to be expected in London at regular intervals.

"Four murders on the same day in London would be expected to occur about once every three years, and it has done," says Spiegelhalter. "Seven days without a murder should occur about six times a year, and it does."

The Significance study was written in conjunction with the Risk and Regulation Advisory Council (RRAC), a government body set up to consider appropriate public response to risk. According to the prof's research, covering crime since April 2004, there has been little change in the capital's murder rate over the past five years.

But you wouldn't know it from reading the news. On 28 July 2008 thelondonpaper had the front-page headline "London's murder count reaches 90". But Spiegelhalter states that this number was normal for that time of year.

"We focused on London for this report as there is a general feeling, often driven by the media, that over the last 12 months murders have increased more than would be expected," he said.

"Those in authority need to remain level headed and offer the general public a thoughtful, proportionate response," said Rick Haythornthwaite of the RRAC. "Sensible decisions can be made whilst never forgetting that each individual case is of course shocking and a tragedy for those affected."

The research can be read in full here (free pdf download available, as of going to press.) Prof Spiegelhalter and his colleagues also have a dedicated site, here. ®