A study by doctors into the attendance of children at hospital emergency departments has revealed that numbers dropped by almost a half on the weekends when Harry Potter books were released. The research, published today in the British Medical Journal, suggests that the boy wizard’s adventures are directly responsible for keeping accident-prone children out of hospital.

Doctors at the John Radcliffe Hospital, Oxford, investigated the impact of the last two books by J. K. Rowling — The Order of the Phoenix and The Half-Blood Prince — on children’s traumatic injuries.

The team reviewed all children aged between 7 and 15 who attended their emergency department with sprains, fractures and other musculoskeletal injuries on the weekends when the books were published. The Order of the Phoenix and The Half-Blood Prince went on sale at one minute past midnight on Saturday, June 21, 2003, and Saturday, July 16 this year respectively. The researchers found that the average attendance rate at John Radcliffe during non-Potter year summer weekends was 67, while on the Potter weekends it was 36 and 37 respectively.

At no other point during the three-year surveillance period was attendance that low. Data supplied by the Met Office for each of the weekends suggested no confounding effect of weather conditions. The research, an idea from a doctor who witnessed how his five children fell under the spell of the books for days at a time, is a further indicator of the phenomenal impact of Harry Potter.

Since the first book was published in 1997, the series has sold 270 million copies in 62 languages in most countries of the world. Earlier this year The Half-Blood Prince, the boy wizard’s sixth outing, sparked the biggest book-buying frenzy in history. More than two million copies were sold in 24 hours in Britain alone.

Stephen Gwilym, specialist registrar at the department of orthopaedic trauma surgery at John Radcliffe, said that the Potter effect made a huge difference to the trauma workload. “I was working those weekends and the difference was really noticeable,” he said. “We normally have to admit about 10 per cent of children who come to A&E during a weekend.

“Each one of those takes an hour of our time. You are talking about a difference of about five hours’ work, which we spent working through cases of older people without having to rush off to A&E to assess and triage children.”

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The publisher Bloomsbury shares rose from 105p in 1994 to 376.5p in 2005

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