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Alas, I have treated the Placebo effect too uncritically in my health econ class. I’ll do better next year. From Wikipedia:
The original 1955 article of Beecher "The Powerful Placebo" claimed a 35% placebo effect in 15 studies. The original article was in 1997 re-analysed and "no evidence was found of any placebo effect in any of the studies" used by Beecher. … The claimed "effects" were produced by spontaneous improvement, fluctuation of symptoms, regression to the mean, additional treatment, conditional switching of placebo treatment, scaling bias, irrelevant response variables, answers of politeness, experimental subordination, conditioned answers, neurotic or psychotic misjudgment, psychosomatic phenomena, misquotation, etc. …
Hróbjartsson and Gøtzsche published a study in 2001 and a follow-up study in 2004 questioning the nature of the placebo effect. … They performed two meta-analyses involving 156 clinical trials in which an experimental drug or treatment protocol was compared to a placebo group and an untreated group, and … found that in studies with a binary outcome, meaning patients were classified as improved or not improved, the placebo group had no statistically significant improvement over the no-treatment group. Similarly, there was no significant placebo effect in studies in which objective outcomes (such as blood pressure) were measured by an independent observer. The placebo effect could only be documented in studies in which the outcomes (improvement or failure to improve) were reported by the subjects themselves.
HT to Brandon Reinhart.
Elusive Placebos
@BrandonOne particular bias appears to be that in many of these studies the subjects are asked how they feel and usually answer in the positive giving a subjective result that isn't really that useful
A lot of outcomes in medicine are inherently subjective.Pain is _SUBJECTIVE_. If anything, the fmri studies on pain seem to indicate there probably is a role for psycho-somatic (placebo) control of pain. There is no physical measurement available. Depression is subjective, there is no know physical measurement available. Chest Pain (Angina) to some extent is _subjective_. Many interventions in medicine are aimed at improving these subjective measures as these things really can effect quality of life. You need a control arm. You need a control arm that doesn't have built in expectations to the questions they are going to answer.
I can't tell - is the claim here that placebos are less effective remedies than previously thought (and completely ineffective for many conditions), or is it that they have no medical benefit whatsoever and only influence what people say about their health? The latter conclusion seems unwarranted, especially given the physiological research that is starting to look at the effects that placebos have on the brain (especially in the processing of pain). I'm not an expert on this, but it looks like these studies are finding effects on lower-level brain processes (like sub-cortical mu-opioid receptors and P2 ERPs) that are inconsistent with a mere reporting bias.