Imagine a world. Lets call it Threa. In Threa there are religions, for the same reason that in this world people are superstitious about walking under ladders or the number 13. Superstitions start because two things that are not connected seem to be once or twice and people make a rule from that.

Now, these people pray to God because their dogma says that prayers are answered, but of course we know that on Threa there is no God. People get ill and die on Threa, but there are doctors that can make people better. Doctors on Threa can't cure everything, though, and they don't know what causes all conditions.

Let us consider a group of churchgoers. They are mutually supportive. They feel the kindred in believing in the same thing. People in this church group get ill, like all others. So they pray to become better, and other churchgoers pray for those that are ill.

Some of the Churchgoers become better. Some don't. Of the ones that get better some get much better. In some cases people become better despite the fact that the doctors cannot give them a reason why. Some of those that get better only get a little better.

The people who don't get better either stay the same and keep the condition for the rest of their lives, and some get worse. Some even die from their illnesses.

The churchgoers all say that their prayers are answered.

Now, let us compare this group with a group of non-believers. They get ill, like the churchgoers, but no one prays for them.

Some of these non-believers become better. Some don't. Of the ones that get better some get much better. In some cases people become better despite the fact that the doctors cannot give them a reason why. Some of those that get better only get a little better.

The people who don't get better either stay the same and keep the condition for the rest of their lives, and some get worse. Some even die from their illnesses.

There are scientists on Threa. They have access to the medical records. They point out that there is little difference in the rates of being ill/getting better between the two groups.

Believers dismiss this, saying that the scientists could be wrong and that the power of prayer cannot be tested by science, it is a spiritual thing. They point out the times when they have prayed for individuals and that person got better.

The non-believers just think it is funny that they have no evidence for their belief in prayer. They can also point out times when non-believers got incredibly better without prayer. The evidence shows that praying makes no apparent difference to whether they got well compred with non-believers, so they might just as well not prayed.