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People going to Lourdes sometimes return and tell stories about a miraculous healing they have witnessed. Do visitors of Lourdes experience spontaneous recovery more often than would be expected by chance?

(Question motivated by meta discussion, I think it is one of real questions people with Catholic background ask, and I would like to see it answered.)

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    Believers don't ask questions. It's the nonbelievers who do. – user unknown Jul 17 '11 at 21:38
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    @User: (not a joke) This is a significant claim with no references. I would downvote this comment if I could. See also meta.skeptics.stackexchange.com/questions/13/… – Suma Jul 17 '11 at 21:47
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    If you assume Sklivvz's answer to be right, there are nearly no witnesses, but millions of visitors. What do they do to answer their question? I have met a lot of catholic people, and a big part of them isn't interested in the truth, but they visit such sensation points anyway. Either they enjoy being together with other catholics, performing prayers and so on, or they feel pressured by the group to visit such places. But they don't try to answer the question, they don't ask for evidence. They don't like to hear it is fraud either - they prefer a vague `unknown' state. – user unknown Jul 17 '11 at 21:56
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    People are not black and white. Sometimes believers doubt, sometime believers become nonbelievers (and vice versa), sometime it is nonbelievers who act dogmatically and do not ask. – Suma Jul 18 '11 at 12:26
  • Yes, I know. I didn't want to give the impression, that my declaration fits everybody, and think, the same is true for you too. – user unknown Jul 18 '11 at 13:02
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"The spontaneous remission rate of all cancers, lumped together, is estimated to be something between one in ten thousand and one in a hundred thousand. If no more than 5 percent of those who come to Lourdes were there to treat their cancers, there should have been something between 50 and 500 'miraculous' cures of cancer alone. Since only three of the attested 65 cures [accepted by the R C Church as miraculous cures] are of cancer, the rate of spontaneous remission a Lourdes seems to be lower than if the victims had just stayed at home."
—From Carl Sagan, The Demon-Haunted World p. 221.

I will reconstruct the references independently because the book has a very poor references section.

  • spontaneous remission of cancer can be estimated between 1 and 10 cases every million (so it's much rarer than Sagan assumed) (source)
  • it is estimated that 200 million people have visited Lourdes since 1860 (source)
  • there are 67 recognised "miracle healings" at Lourdes, of which only 5 are cancer-related (source)
  • cancer accounts for way more than 5% of deaths, so we can assume it's an underestimation. From here we can verify that at least 16.8% of male deaths and 11.7% of female death are due to cancer, at least in UK.

There is no particular preference for cancer victims to go to Lourdes over victims of other illnesses, so we can estimate that at most 12-17% of the critically/terminally ill are there for cancer-related reasons (one of the preconditions for a "miraculous cure" is a diagnosed disease).

Not all people go to Lourdes for a terminal illness though, so the more conservative 5% figure that Sagan provided potentially compensates for this.

In other words, if 5% of people coming to Lourdes are there to cure cancer, then their number would amount to 10 million people.

Out of a set of 10 million cancer victims, we should normally expect between 10 and 100 cases of spontaneous remission of the disease, statistically speaking.

However, only 5 cases of "cancer miracles" are reported from Lourdes, making the healing powers of Lourdes statistically insignificant over pure chance.

Most of the other alleged "cures" are pre-1970 and related to TBC and MS, which are now either curable or known to have high rates of temporary remission. Funnily enough, the number of alleged "cures" has diminished as medical science has learned to heal patients of the most common ailments and to properly diagnose common remissions.

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    I never thought I'd say this, but very nice job clarifying Sagan – Monkey Tuesday Jul 17 '11 at 23:25
  • +1 That's a great approach. The 5% figure sounds plausible, but I am wondering how you chose it. – Oddthinking Jul 18 '11 at 0:51
  • @odd I used Sagan's figure. It's much lower than the incidence of cancer on mortality, but it also accounts for past mortality figures when TB was the big killer. A low number makes the healings more significant, by the way. – Sklivvz Jul 18 '11 at 5:48
  • Still, the 5 % seems just a guess and one can easily imagine it could be even less in reality. Are there any statistics which could be used to make this guess more reliable, e.g. relative amount of cancer compared to other mortal or serious diseases in a normal population? – Suma Jul 18 '11 at 9:44
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    @Suma: it's a guess but cancer accounts for way more than 5% of deaths, so we can assume it's an underestimation. From here you can verify that at least 16.8% of male deaths and 11.7% of female death are due to cancer, at least in UK. – Sklivvz Jul 18 '11 at 12:35
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Lourdes receives over 80,000 pilgrims a year, of whom approximately 7000 people in more than a century have sought to have cures confirmed as miracles. Terrence J. McNally says in What Every Catholic Should Know About Mary, page 28, that only 68 of these have been declared as scientifically inexplicable by both the Lourdes Medical Bureau and the Catholic Church, a number so small as to suggest that these cases were likely to have been cured or gone into remission anyway. On this view, the cures or remissions were entirely by chance, without even a placebo effect.

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