What’s so good about evidence?

An odd question, you might think. But actually, evidence in the sense of trying to arrive at “evidence-based policy” is a lot less straightforward than it might sound. Along with motherhood, apple pie and one or two other items universally agreed to be good things (without any evidence, of course) evidence seems an indisputably good basis for policy development.

And just at the moment, evidence-based this, that and the other are making several simultaneous appearances. The Government’s decision to relax the prescription obliging them to appoint certain kinds of scientist to the Advisory Committee on the Misuse of Drugs (ACMD) has rekindled the great Nutt debate, and led to accusations that this is merely a ploy to avoid creating an evidenced-based drugs policy, and instead allowing, well, I suppose, a prejudice-based policy. The Justice Secretary Ken Clarke is embroiled in a spat with his more right-wing colleagues about whether or not “prison works”, and is sounding considerably more liberal than his Labour predecessors by the outrageous novelty of actually looking to see if there is an answer to the question hidden, or in this case not very hidden, in the evidence. Today we hear that, in contradiction to previous evidence, the balance of opinion on the advisability of prophylactic low-dose aspirin for just about everyone over 45 has now shifted decisively in favour.

In these three disparate examples we can discern some of the problems inherent in this “evidence, good; everything else, bad” doctrine. In the misuse of drugs case, the issue is simply that drugs policy has nothing to do with harm (which is what the evidence is all about) and everything to do with what might be termed social discipline. On the latter evidence has nothing to say. In my view it would be better to disband the ACMD altogether than to continue to have it grace the fiction that harm is the issue that drugs policy is designed to address. It’s plain to see that it isn’t. From a harm perspective, we’d move to prohibition of alcohol. I seem to recall that that’s been tried somewhere at some time, and the, er, evidence is that it wasn’t a great success.

In the prison working or not working business, we all know that it doesn’t. At least, it doesn’t if by working we mean that those who’ve broken the law are, through the medium of prison, rendered less likely to repeat the experiment. But everyone knows that this isn’t what prison is for anyway. Prison is there to keep offenders off the streets for a limited time, and to make the public feel that obeying the law is being properly encouraged by the sight of what happens to those who don’t. Sad to say, by that criterion the evidence indeed shows prison is a great success, and the public can’t get enough of it. Mr Clarke’s sudden conversion to evidence is not related to whether prison works or not, but to the equally abrupt realisation that it’s too bloody expensive.

Aspirin has some very beneficial effects, and some deleterious ones. It’s all about the relative balance of the former versus the latter. This is evidently a tricky balance to arrive at since it’s been argued both ways in the very recent past. The evidence changes over time, which is no more or less than one would expect. Unfortunately, even in this example when one would have thought that evidence would reign supreme and without controversy, it shows its weakness. Aspirin needs time to weave its magic, and quite a long time it would seem. Somewhere between 4 and 25 years. Within which time we’d have been taking it, spitting it out, taking it again, spitting it out unless we’re already nearly dead, and now lapping it up as if there were no tomorrow. Not such a simple guide to policy, then.

Of course I am not suggesting that evidence is not important. But it isn’t without its problems, and it is not at all obvious to me that it’s the only, or even the best, guide to public policy. A better guide is honesty. Honesty about what the purposes of policy really are. Honesty about what, if any, place evidence can, or should, have in debates about policy. As it is, evidence is simply a modesty screen wrapped in front of policy makers to obscure their real motivations.

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2 thoughts on “What’s so good about evidence?

  1. Prison is there to keep offenders off the streets for a limited time, and to make the public feel that obeying the law is being properly encouraged by the sight of what happens to those who don’t. Sad to say, by that criterion the evidence indeed shows prison is a great success, and the public can’t get enough of it.

    Is b) a legitimate policy goal? I don’t mean “is it popular”, because it is. I mean “is a policy that does nothing but harm to society, apart from making people who don’t know any better wrongly think that it’s helping” legitimate for people who know that it doesn’t work to pursue under the pretence that it does work?

    Which I suppose is the same questions as “is it legitimate for a doctor to prescribe a patient a placebo without telling them”?

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