The randomised control trial at three West Midlands hospitals is only half way through.

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"This is a randomised clinical trial which is the gold standard for producing evidence, " she added.

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The researchers at Harvard couldn't run a randomised controlled trial where half the participants ate burgers for two decades and the other half didn't, but they could use statistical techniques as the next best thing.

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This was done by comparing data with findings from the Randomised Badger Culling Trial (RBCT).

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But not everyone's convinced by this reworking of the Randomised Badger Culling Trial with the benefit of hindsight.

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We've learnt from the lessons of the Randomised Badger Culling Trial and turned it into a policy that can be delivered and gives us the benefits of culling in the long term.

BBC: Badgers back in the firing line

But the major UK investigation, the Randomised Badger Culling Trial (also called the Krebs trial), showed culling only produced a benefit if conducted rigorously and systematically over large areas, ideally with hard boundaries that badgers could not cross.

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That was the emphatic, and damning, conclusion reached by Professor John Bourne, the man charged with assessing the biggest and most comprehensive scientific experiment ever conducted in the British countryside - the Randomised Badger Culling Trial, or RBCT, in June 2007.

BBC: Badgers back in the firing line