Leading statistician Professor David Spiegelhalter claims today that the number of murders in London last year was not out of the ordinary and followed a predictable pattern.
Spiegelhalter's report, published today in Significance , the magazine of the Royal Statistical Society, argues that shocking headline numbers are not as surprising as one might think.
Violence in London attracts headlines. After four people were murdered in separate incidents in London on July 10th, 2008, BBC correspondent Andy Tighe said "To have four fatal stabbings in one day could be a statistical freak." But could it? On July 28th thelondonpaper had the front-page headline: "London's murder count reaches 90". But Professor Spiegelhalter states that this number was predictable.
"Murders in London follow a random pattern that makes certain aspects predictable and so we can fairly accurately predict the number of murders there will be as the year progresses," explains Spiegelhalter, the Winton Professor of the Public Understanding of Risk at the University of Cambridge. "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."
Spiegelhalter continues, "We counted how many murders occurred on each day over a three-year period. Four murders on the same day in London would be expected to occur about once every three years, and it has done. Seven days without a murder should occur about six times a year, and it does." Each murder is an unpredictable event, and the report does not imply that specific events can be predicted, only that the overall patterns are remarkably predictable. "Tragic though every murder is, these numbers are not surprising, and there's no evidence of an increasing murder rate."