I'm not a fully-signed up fan of "evidence-based politics", which you might find odd, since I'm a statistician. It's because it's often used to mean "I've found a small sociological study which supports the belief I had anyway, and I'm now going to call that study proof that I am right, and label anyone irrational if they don't agree with me about the science." Applying the definite article in front of the word "science" is the fastest way to make me suspect you're trying to shut down a debate.

Sometimes, though, the evidence comes from a more reputable source: a properly designed scientific experiment. Such is the case with the evidence about the impact of culling badgers on the incidence of bovine TB. I'm a little shocked to find, via googling, that I first wrote about this in 2008, more than three years ago. After all that time to review the scientific literature, DEFRA is now suggesting that farmers should be allowed to shoot badgers more or less at random, if anything a worse proposal than a total cull. With apologies, this is a black-and-white issue.

The Independent Study Group on Cattle TB (ISG) presented its final report (to David Miliband: remember him?) in December 2007. To say that the statisticians who took part in the work of the ISG are eminent is like saying David Beckham is quite a well known footballer. Christl Donnelly, George Gettinby, and especially Sir David Cox FRS, are statistical royalty. They were core members of the ISG and assisted with the design, analysis and interpretation of the studies the group commissioned into whether or not badger culling would have a positive impact on bovine TB.

You can read the full report here. It's worth reading this paragraph from John Bourne, ISG Chairman, in his overview to the Environment Secretary:

'The ISG's work - most of which has already been published in peer-reviewed scientificjournals - has reached two key conclusions. First, while badgers are clearly a source of cattle TB, careful evaluation of our own and others' data indicates that badger culling can make no meaningful contribution to cattle TB control in Britain. Indeed, some policies under consideration are likely to make matters worse rather than better. Second, weaknesses in cattle testing regimes mean that cattle themselves contribute significantly to the persistence and spread of disease in all areas where TB occurs, and in some parts of Britain are likely to be the main source of infection. Scientific findings indicate that the rising incidence of disease can be reversed, and geographical spread contained, by the rigid application of cattle-based control measures alone.'

I don't really think it's worth trying to rephrase that, as the statement and the evidence which supports it are as clear as day. But let me try: The culling of badgers is a psychological displacement activity, which will needlessly increase the amount of suffering on the planet. That's bad enough. But it won't keep cattle free from TB either.

I can't remember the last time a policy managed to be irrelevant, malicious and ineffective, all at the same time. Sometimes - I was going to write "politicians", but that's unfair, we all do this - sometimes we wish for something so much that we refuse to notice that the actions we're taking will actually prevent our desire from coming into effect. Something like that is happening here, I think.

Caroline Spelman - it was quite hard to convince people that selling off forests made sense (you did convince me). If you permit random culling of badgers to go ahead, you'll look back at the forest sell-off U-turn with fondness, I think. Please make use of the world-class, first-rate, independent scientific work that has been carefully done on this subject, and ask both DEFRA and the NFU to think again.