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“It takes more than a swallow to make a summer”
There are numerous positive studies on homeopathy! This argument is regularly put forward by advocates of homeopathy. The conclusion is then drawn that the effectiveness of homeopathy has been proven. The argument is correct, but the conclusion is wrong for several reasons.
There are currently about 400 clinical studies on homeopathy. Assuming that homeopathics are pure placebos, about 20 studies must be positive by chance alone in the case of common error probabilities. This number could increase considerably if one considers that negative studies often remain unpublished. This phenomenon is known in science as “publication bias” and has been well investigated.
But that is by no means all. We know that methodologically weak studies are more likely to produce positive results than methodologically sophisticated studies. It is therefore obvious that the positive studies are on average less reliable than the studies that do not prove the effectiveness of homeopathy. In addition, many of the methodologically cleanest homeopathic studies, e.g. those from the homeopathic hospital in Glasgow, do not actually examine homeopathy but isopathy; i.e. they are not based on the principle of similarity which is essential for homeopathy.
Finally, it should be emphasised that for a truly reliable assessment of therapy, not only individual studies should be selected, but the totality of all high-quality studies, i.e. systematic reviews, should always be taken into account. Summaries of all methodologically acceptable studies generally come to the conclusion that the effectiveness of homeopathy has not been proven.
The only (not very surprising) exception is reviews published by homeopaths on the basis of pre-selected studies. The most recent of these publications conclude that homeopaths are marginally better than placebos. But even these authors (paid for by homeopathic organizations) have to admit that
“The poor or unclear quality of the evidence requires caution when interpreting the results”.
However we turn it around, the current state of studies does not prove the effectiveness of homeopathy. And there should be some reason to think that this has not been achieved in over 200 years. Homeopaths earn their living by claiming the opposite – perhaps everyone has the right to their own opinion, but certainly not to their own facts!
(Author: Edzard Ernst, Emeritus Professor, Uni Exeter, UK)