Lies, damned lies and statistics - Guardian
"It is possible to be very unlucky indeed. A nurse called Lucia de Berk has been in prison for five years in Holland, convicted of seven counts of murder and three of attempted murder. An unusually large number of people died when she was on shift, and that, essentially, along with some very weak circumstantial evidence, is the substance of the case against her.
She has never confessed, but her trial has generated a small collection of theoretical papers in the statistics literature, and a government inquiry will report on her sentence in the next few weeks.
The judgment was largely based on a figure of "one in 342 million against". Now, even if we found errors in this figure, the figure itself would still be largely irrelevant. Unlikely things do happen: somebody wins the lottery every week; children are struck by lightning.
It is only significant that something very specific and unlikely happens if you have specifically predicted it beforehand."
It's well worth reading the whole of this thoughtful article.