The irony is that scientists are much less certain about what they say than politicians, policy-makers, and pundits. The certainty of the kind you see in the face of a politician declaiming on tax increases or hear in the voice of a commentator condemning or endorsing a foreign-policy decision, or the certainty you detect in the words of an op-ed writer pontificating on one thing or another – I used to think that they arrived at their certainty after considering an issue in great depth and finding that the evidence fell overwhelmingly in favour of a specific position. You must think me naive ever to have thought this way. But I did. I used to think that a good argument was the midwife to certainty. If, as I now believe, it is the wish that fathers the thought, then certainty is the lingering imprint of a wish on thoughts and arguments, like DNA retained in progeny, acting invisibly but with visible effects.
See also policy-based evidence.