The agonies of evidence

John Maynard Keynes argued that politicians don't like evidence. It ties their hands. I once quoted this when introducing a government minister, who was opening a conference on research. “Balls,” she answered. But this week's BMJ illustrates how evidence can complicate the lives of politicians.

The arrival of a Cochrane review suggesting that mammography did not save lives but simply increased mastectomies must have been painful for those who have invested heavily in screening programmes (27 October, p 956. The British government doesn't accept the results of the …