There have been two reactions to the most recent large study of intercessory prayer. Both have missed the point. Atheists have pointed to the fact that it shows no benefits at all for the recipients; believers have said that this won’t stop them praying; that they know of plenty of cases where prayers have been followed by an improvement in the patient’s condition, ergo prayer works.

None of this tells us anything we didn’t know before about the way the world works (and prayer doesn’t). But there is one real new fact that the study reveals which seems to have escaped attention; and this is that Americans, by and large, don’t really believe in God. To understand why, you have to look at the oddest feature of the whole thing, which is that being prayed for, and knowing that you were being prayed for, actually increased the risk of complications among patients recovering from heart surgery.

This was explained by one of the authors of the study as a consequence of anxiety – that, when people heard they were being prayed for, they naturally assumed that things were terrible, which made them more anxious, and, in some, brought on a heart attack. But why is this the natural assumption? If prayer worked as a placebo, you would expect things to get better.

There is a story which I heard¹ from the late Pat Wall, a pain researcher, which casts light on this. In the late Fifties, when human experimentation was easier, there were a couple of experiments carried out, at Harvard and the University of Pennsylvania, to test the efficiency of a treatment then popular for angina.

Angina is a painful, sometimes deadly condition caused by an insufficient blood flow to the muscles of the heart, so in the Fifties it was quite common to close the nearby mammary arteries in the belief that the blood thus diverted would make new channels though the heart muscle. Of course, this didn’t happen, but many patients were helped by the operation anyway.

So two experiments were carried out, in which patients all had their chests cut open and the mammary arteries exposed, but only one group had anything done to these exposed arteries. The result was completely baffling. "The majority of both groups of patients showed great improvement in their amount of reported pain, in their walking distance, in their consumption of vasodilating drugs, and some in the shape of their electrocardiogram." The improvement was maintained for six months.

This was told by Dr Wall as a story about the power of the placebo effect. In fact, as we know now, both treatments were useless. Yet both produced measurable, lasting physical improvements in the patients, because they believed in them. When they were told that they were getting an operation which would improve their heart function, they expected medical science to deliver, and it did. No one had to have faith in medicine. They just believed.

The contrast with the prayer study could not be greater. The knowledge that patients were being prayed for worked on them as a nocebo – the malign opposite of a placebo – and in this revealed more clearly than any other experiment could the fact that Americans, even devout Americans, don’t really expect prayer to change the world, and certainly don’t expect it to substitute for medicine. It may be that only two or three or per cent of Americans call themselves atheists but it looks as if the vast majority of them effectively are.

I suppose the really interesting experiment now would be to try offering post-operative patients "healing crystals" and seeing what difference the knowledge of those things made to the outcome. I doubt it would even have a nocebo effect. I suspect that everyone knows these things are just harmless fun. But I also doubt the Templeton people would fund it, as they did the heart study.

¹ 1993 Experimental and theoretical studies of consciousness. Wiley, Chichester (Ciba Foundation Symposium 174) p187-216