The need for evidence

Sense About Science is conducting a campaign in favour of evidence-based policy making. They asked members of the public to say why evidence is important to them. Here's what I wrote:

Elected politicians are expected to claim total knowledge when seeking election. Any such claim falls somewhere between optimism and dishonesty but after a time politicians come to believe their own words. Attention to evidence is needed as a corrective to this 'optimism'.

But it's also essential if we want policies to work - ie achieve their stated goals. There are almost always conflicting opinions about the likely effects of a policy but an opinion is what you have when you lack knowledge. So to have the best chance of working policies need to be based on the best possible understanding of the situation. That requires evidence and sometimes trials of several policies to see what works.

This is demanding. it requires what Russell called humility in the face of the universe. To attend to the facts and not to ones own prejudices. It also requires a kind of political courage. To be willing to say to the public and the press "Actually, we don't know what would work best - but we are determined to find out!"