If a randomized controlled trial includes just two groups, one which gets a treatment and another which gets placebo, it cannot attribute any results to the placebo, because it's missing a control for the placebo, i.e. a group which gets no intervention at all. Many studies have made this error, but that doesn't mean there's never a placebo effect.
I don't disagree exactly about missing a control for the placebo, but I think a control for a placebo is logically impossible, and therefore nobody has ever, or can ever, measured a placebo effect. Does that mean "there's never a placebo effect"? That's a philosophical question.
> I don't disagree exactly about missing a control for the placebo, but I think a control for a placebo is logically impossible, and therefore nobody has ever, or can ever, measured a placebo effect.
The control for a placebo is no intervention, and not only has placebo effect been measured, but differential placebo effects by administration method have been measured (a placebo treatment that involves piercing the skin, for instance, has a bigger effect than a pill.) This is why a valid placebo needs to match administration method of the intervention being tested.
There is no way to coherently define the "placebo effect".
When you test a treatment vs. placebo, and speculate that there is a "placebo effect", it means that you are supposing that lying about treatment produces a therapeutic effect.
But you can't test a placebo vs. nothing, because a placebo is not a treatment, and nothing is not a placebo.
Giving a sugar pill and disclosing you are giving a sugar pill is not the same thing as lying about treatment (unless the recipient believes it is efficacious). Lying about it being efficacious doesn't help your experiment unless it's a credible lie.
Giving "nothing" cannot be a control because it is obviously different from a sugar pill. So you cannot do a blind test.
The idea of testing a placebo effect is an epistemological morass.
That study wouldn't be checking placebo but whether the intervention beats placebo. Not sure why that's a mistake if measuring placebo is not a research goal.
The mistake would be attributing any outcome to the placebo intervention. The mistake isn't in the construction of the experiment, but in the interpretation of its results.
the placebo effect is both larger and smaller than people intuitively assume.
it's larger in the sense that part of it is essentially impossible to control for; people in a clinical trial are predisposed to, at a minimum, think about the issue which is being investigated, which likely causes some sort of change in their mindset and subsequently their body. there's no real way to measure that adequately.
but it's smaller in the sense that the body isn't a system like in the Matrix where "the mind makes it real". if someone tells you that you drank lethal poison (but in actuality you drank a placebo), you might feel bad, but you won't die. the reverse is not necessarily true, bizarrely.
if you get a (unbeknownst to you) placebo/sham knee surgery as part of a trial to investigate the merit of a genuine surgical procedure designed explicitly to reduce pain, it'll reduce your pain almost as effectively as "the real deal". but here's the clincher. if you are told beforehand that it is a placebo, it'll still reduce your pain, although if i am remembering the study correctly it was a smaller benefit than those who were not told they received a placebo.
so if you know you're getting a placebo, the effect is WAY larger than it "should" be. but that's for a subjective variable -- pain. but when the subject isn't prompted about the effects of the placebo, or is administered a totally implausible placebo which can't possibly fix the issue -- like a pill to cure a severed arm -- it's even more impotent than we would expect.
I am not sure why you have been downvoted. Yes the placebo effect is often just a regression to the mean of a condition that varies. Imagine that you have a disease that goes up or down in serverity (say depression). People enter the trial when most ill and over the course of the trial they trend back to symptomatic mean (i.e. they get better on their own). This is why doctors favourite treatment "let's wait and see" is so effective.
http://www.dcscience.net/2015/12/11/placebo-effects-are-weak...