any wonderful results are attributed to the "placebo effect" (Amos)

That's simply not true. If in a test of any healing method (alternative or not) the group that gets nothing (or the opposite of the treatment) but is led to believe it gets the treatment performs as good as the group getting the treatment but both perform better than people getting nothing (and knowing about it) then the effect is called placebo effect. Any wonderful cure doing better in the treatment group would not be attributed to the placebo effect.

And that is just a term, as Clint says, far from any explanation yet. But it is a term very useful in grouping things together that display similar characteristics, namely that the result seems to depend only on the patient believing the action has been done and not on doing the action as such. What is dismissive about using the Latin term for 'I shall please' to group these things together I am not able to understand.

The term placebo effect is extremely helpful when talking about studies in psychology or medicine. A recent survey about the effectiveness of psychological interventions of all kinds has listed the effect sizes of the intervention. The effect sizes ranged roughly from -.2 to +1.3 standard deviations with a maximum at about .6 standard deviations. It is then very useful to break up these studies into studies using a no-treatment control and those using a placebo control. The effect sizes were .3 on the average with a placebo control, smaller than with a no treatment control but still significant. If anyone at a congress tells she has found an effect size of her intervention of .8, the first question (if she hasn't told) is what was her control group (placebo, wait list, no treatment?).

Any person with a bit of responsibility would like to know whether a treatment works even if the patients are told they are not treated, when the effect is larger than placebo alone. As a doctor I'd like to know whether a medication I give has been shown not to work better than a placebo control, especially if that is a medication with side effects. If it doesn't work better than a placebo control but has side effects I'd choose something harmless and cheap instead for that has the same potential effect.

Behind the classification 'placebo effect' are lots of potential really causative agents. People are doing a lot of work to find them out. That's very useful in order to know when this effect may be useful. Contrary to popular belief, the placebo effect is very close to nil with life threatening illnesses when there are objective indicators of the state of health. Don't expect any help from placebo effects when you have an appendicitis.

It has a much larger effect when the state of health has a strong subjective component, e.g. chronic pain. If it helps in these situations it is preferable to a long-time use of pain killers. A good doctor would give a patient in this situation first pain killers and then say that it would be good to reduce the dosis for the sake of the liver and to learn to cope a bit with the pain. And then he'd reduce the dose to ever smaller levels up to nil, if the patient reports she can cope now.

The placebo effect is not only found to be restricted to health. For instance, take an additive for petrol to make it last longer or a very cost consuming apparatus to reduce the lime in the water coming to your house. How do you get a placebo effect here? Easyly, by using a subjective outcome measurement. You ask the person if the water now tastes better or if she feels she lasts longer with on tank filling. With such a dependent variable, you will have a positive effect of the intervention. But wouldn't you like to know before whether the costly action works better than a placebo control?

Wolfgang