Palestinian women praying in Jerusalem

The tests used crude methods, concluding for instance that prayer was proved by the long lifespans of royals - people who were much prayed for. These methods have been superseded by more rigorous trials.

But, remarkably, many modern tests have reached similar conclusions. Professor Leslie Francis of the University of Bangor has studied 31 experiments (conducted to the "highest professional standards") into the effectiveness of prayer.

The trials would typically take a group of hundreds of patients recovering from heart surgery, randomly divided into two groups, one of which is prayed for. None of the patients would know they were or weren't being prayed for.

It depends on God being an intervening God

David Laws

"The findings are quite staggering," he says. "Studies show that patients in hospital who are being prayed for (even when they do not know they are being prayed for) are more likely to recover."

But according to Dr David Laws of the University of Manchester the kind of prayer which asks God to do something is only relevant if you have a particular understanding of God.

"It depends on God being an intervening God who breaks into our world and mops up our mess whenever we make one."

Jews praying at the Wailing Wall in Jerusalem

That is a kind of God that Professor Francis says he would be uncomfortable with, since it raises questions that if God can intervene, why does he not do so to avoid more human suffering?

But former cancer patient Mary Ligertwood, from Milton Keynes, believes prayer did play a part in her recovery.

When she was found to have cancer in her breast, kidney and lymph gland at the age of 50, she was given a year to live. And yet within six months, she walked away free of the disease.

People would ask me: 'Why are you so happy?'

Mary Ligertwood

Now 13 years on, she puts her recovery down to a combination of the power of surgery - she had five operations - and the prayers of her friends. But she does not consider herself to have experienced a "miracle cure".

She does though consider it a miracle that the whole experience of diagnosis, surgery and recovery was for her such an enjoyable - and spiritual - one.

"Again and again, people visiting me in hospital would say: 'Why are you so happy?' For me it really was a very wonderful time... There was no element of fear there at all."

Peace prayers

The inner effect on praying people has a bearing on prayers for world peace such as those said at Assisi, says Dr Laws.

"For me it's not a matter of persuading God to do something, but of people praying for peace looking to become peaceful people. It starts with the internal effect and that, hopefully, will have an impact on the outside world."

I'm not surprised research shows an impact on people who are praying. But the studies also show an impact on people who are prayed for

Leslie Francis

Lord Hylton says the fact of the religious leaders praying together was a significant statement in itself, and one which has made its own contribution to a more peaceful world.

In particular, he says, a declaration the leaders made that their religions should not be used as pretexts for violence or wars could have a huge impact. He believes that even now, the religious leaders in the Middle East have become more inclined towards engaging with each other.

Professor Francis suggests that should another day of prayer for peace be organised, subsequent levels of fighting should be monitored, as should people's perceptions of peace.

Many religious people may feel however that having tangible proof is not really what prayer is about, and that - believe it or not - they rather enjoy simply believing.

What are your views? Send them to us using the form below.

Some of your comments:

Looking for a response a month on, after only one day of prayer? If we want God to supernaturally act in our world, we need to show Him we're serious and pray regularly, hard and long!
David Slater, Scotland

I don't believe in God but I believe in the power of prayer and often ask my Mum, a catholic, to light a candle or "say one" for people I care about who are ill or having a tough time. I don't think you have to believe in a particular higher power to benefit from praying - which is simply a form of meditation or channelling your thoughts and energies.
Sarah Wilson

Prayer is not only a complete waste time, it's also degrading.
Derek Watson

I wish these people would get real. The sooner people understand that we are on our own, and that when things go badly praying to some mythical concept of a 'creator' isn't going to do anything. Think for yourselves and act for yourselves. Is this the dark ages?
SK, UK

What we can never know is how much worse things might have been had we not been praying.
Maryla Carter, England

The problem is we mistake praying as some form of 'wish list' to someone up above. The reality is that prayer is more about developing our relationship with God. We don't always see prayer answered but that does not mean prayer does not work.
Mark Wigginton, Leeds, UK

There is no more powerful thing in this world than the power of prayer. I used to be an atheist, but I became a Muslim over 7 years ago. Until you see and understand how prayer and conversation with God can benefit you, and until you notice that a prayer has been answered, you'll never understand its power.
James, UK

Asking "have prayers for peace a month ago worked?" is not a sensible question to ask, as who can tell the timescale God works on? What is certain if you talk to those who know God is that prayers are always answered, but not always in the way we might want or expect. Answers are not always "Yes", but also "No" and "Not yet - wait".
Jenni Sparkes, Britain

Who cares if it works or not? If it makes people feel better by praying then good luck to them. The only downside is if people think that's all they need to do to achieve anything. World peace or anything for that matter can only be achieved by working out what's involved in achieving it, calling that a plan and then implementing the plan. Prayer would only be an optional extra.
Alex Keenleyside, England