[sjf911]

Kind of reminds me of an interview of a survivor of the bridge collapse over the Mississippi recently. She was praising god as he had answered her prayers and saved her all the while, in the background, was a jumble of debris sitting on top of those who's prayers were not answered.
There is not a single unequivocal example of divine intervention of any sort much less prayer anywhere. If there was, belief in god would not require "faith". Certainty in the effect of prayer is an example of the human ability/trait of selective sampling and bias. This is, of course, why the scientific method was invented and why it is so effective.