I've often heard it said that, "Nothing fails like prayer." Why, then, are there so many who attest that they've been healed by God?
Not to worry: I'm not going to go into a long-winded description of confirmation bias, regression to the mean, or the problem of evil.
Why don't we participate in a little thought experiment? They're rather more cost-effective to conduct than the real thing, after all. So: Assume that twenty men are diagnosed with terminal cancer, and that all of them pray for healing. If all but two of them die. So what's our success rate? Ten percent. But these two men who prayed for healing and did not die will in all likelihood report that their prayers were answered, and that God cured them of their cancer. Where are the other eighteen men whose prayers were not answered? They were, unfortunately, unavailable for comment. Our reported success rate? One-hundred percent.
This is why anecdotal evidence is worthless when it comes to objectively evaluating truth-claims. When it comes to prayers for healing, God, in his infinite wisdom, has cooked the books.