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How JK Rowling was unmasked

image captionJK Rowling's secret was uncovered after a Sunday newspaper became suspicious

Prof Peter Millican of Hertford College, University of Oxford, helped unmask JK Rowling as debut crime writer Robert Galbraith.

An expert in computer linguistics, the professor developed software to analyse and compare texts.

He analysed The Cuckoo's Calling against Rowling's other novels, The Casual Vacancy and Harry Potter and the Deathly Hallows.

He spoke to BBC News about how he arrived at his conclusions.

"I was given some text by The Sunday Times - I had two known texts by JK Rowling, two by Ruth Rendell, two by PD James and two by Val McDermid.

"What I did was clean up the texts, put them into my software and do a battery of tests to see what similarities there were.

'Striking' comparisons

image captionProfessor Millican compared word length and punctuation patterns in a series of tests

"I was testing things like word length, sentence length, paragraph length, frequency of particular words and the pattern of punctuation," he explained.

"What was striking about the tests was how often The Cuckoo's Calling came closest to the texts by JK Rowling and it was closer to those than to any other crime novels.

"In the vast majority of these tests I found that the new book came closer to A Casual Vacancy and/or Harry Potter and the Deathly Hallows than it came to the other six books by the other three authors.

"The analysis corroborated quite strongly the hypothesis that had been put to me that she had written [The Cuckoo's Calling].

"Given that there was some independent evidence - apparently - that it was written by a woman, I was comparing it with texts by three other women and certainly, of those four, I had no doubt that JK Rowling was far and away the most likely [author].

"The great virtue of the tests that I was using is that they were based on very generic qualities of the texts, like length of sentences or frequencies of very common words like 'the' or 'to', or 'in', not very distinctive words, and those sorts of patterns tend to be absolutely unconscious to the author and often quite consistent between their texts.

"The conclusion was that on a lot of these tests - surprisingly many - The Cuckoo's Calling came out much closer to the JK Rowling text than to the others.

"Normally with these tests I would try to test novels against each other from the same genre and I found it quite significant that in this case, we had a crime novel which proved to be more similar to JK Rowling's non-crime novels than it was to other authors' crime novels, and I think that does give great significance to the tests."

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