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In a paper defending homeopathy, it is argued that the observed benefits of homeopathic treatments cannot be attributed to the placebo effect because the treatments elicit similar benefits when used on babies and animals, who can have no pre-conceived expectations.

They went on to argue that patients who were cured by homeopathic remedies could very well have been cured without any medicine at all, or the cure was just an effect of their belief in the medicinal efficacy, that is, simply attributable to “placebo effect.” When it is pointed out that homeopathy acts equally effectively in babies and animals, who have no belief or faith in the medicine, challengers also demand a valid explanation for the mechanism of action of the ultralow doses of medicines that could be acceptable within the realm of known scientific knowledge. source

Can the placebo effect be observed in experiments conducted on babies or animals?

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    Related: many of the criticisms of the studies of homeopathy pin the relative efficacy to the better bedside manner of the doctors, the fact they show more interest and so on. Yes, related to the placebo effect, but I don't see why caring for a baby or a pet would not work just as well. – Sklivvz Apr 30 '11 at 23:40
  • @sklivvz - while that is undoubtedly a plausible factor in some studies, it does not account for anecdotal evidence when it's parents who provide the medicine. More on topic, you can easily design a study that would hold such factor constant, but I don't know if existing studies did that. – user5341 May 1 '11 at 0:26
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    Who said the placebo effect is psychological? – Raskolnikov May 1 '11 at 16:01
  • By working equally as well, based off of the statistical data and not the anecdotal... that means not at all? – Mike May 1 '11 at 16:20
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    I'm not sure you can count this as a placebo, but if it's not a double-blind test, the results of the test can surely be biased by the expectations of the person carrying out the test even if it's an experiment on babies or animals. – Andy May 3 '11 at 17:49
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The issue of animals (and presumably babies too) reacting to the expectation of their handlers is known as the Clever Hans Effect.

It is named after a horse that could apparently answer difficult questions, which it did by watching the body language of the (unknowing) trainer.

Because of examples similar to Clever Hans, it is necessary to ensure the people handling the animals are also blinded to the treatment when doing animal trials.

An additional effect to be concerned about is subjective measurements being affected by the expected or desired outcome based on the treatment. ("My dog looks happier ever since the treatment.")

Update: Additional References, in accordance with requests from comments:

Ben Goldacre's Bad Science blog discusses a study in which sniffer dogs gave false positive detections when their handlers believed drugs were present. (From memory, I don't believe the study conclusively showed that the dogs actually behaved any differently; their behaviour may just have been interpreted differently.)

Ben Goldacre's book of the same name has a section on Placebos and Animals.

The Science Based Medicine blog also discusses placebos and animals.

An experiment described in Pyschosomatic Medicine showed how rats could be conditioned to have immuno-response to placebos.

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    That's exactly what's happening. Now a few more references (especially for babies) would be nice. – Lagerbaer May 1 '11 at 15:59
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    "My dog looks happier" shouldn't really be the basis on evaluating medical treatments, unless it's antidepressants. Can dogs have depression, I wonder? :) – user5341 May 2 '11 at 0:47
  • @DVK, Perhaps I overstated the example a little to illustrate my point clearly. However: Yes, there are anecdotes supporting homeopathic treatments for your dog's feelings (e.g. rescueremedy.com/pets/testimonials.asp). Many years ago, one of my family members was researching the effect of antidepressants, using a rat-model. The team had bred rats that showed signs of depression - whether they could really be considered depressed was debatable and not relevant for the research. – Oddthinking May 2 '11 at 3:15
  • Please provide proof oF your statements. As is, it's a conjecture. – Sklivvz May 2 '11 at 3:52
  • Now two people have asked for more references, but I am not sure which statements count as conjecture. The reference I have given defines the term, explains the origin and explains the consequences on experimental effect - i.e. it is a reference to the first three paragraphs. The fourth paragraph doesn't strike me as a conjecture either. – Oddthinking May 2 '11 at 5:17

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