1. Isn't 1 in 49 still hugely statistically significant and therefore suspicious? The probability of this happening by chance is still only 2%
2. What were De Berk's the "great secrets" and "secret compulsion"? Was there any other evidence presented against her besides the raw statistics?
3. In the case of Folbigg I just wonder: Why would she have so many kids if all she does in her diary is complain about their existence ... ??
Imagine someone goes to a casino, and play a game where you flip a coin 20 times in a row, and win if they're all heads. There's about a 1 in 1 million chance of flipping 20 heads - so people are suspicious that the person cheated.
However, imagine that during that same time period, 10 million people played that game. Looking at that, you'd expect there to be 10 winners of the game. Suddenly it's not suspicious at all.
So I think the argument is that this is the chance a nurse experienced this many deaths is 1 in 45 - so with 45 nurses, you'd expect one to experience it.
2% means a false positive for every 50 nurses.