Are double-blind trials underestimating drug effectiveness?
In a double-blind trial, patients exhibit the placebo (and nocebo) effects because of the expectation they might be on a real drug.
If expectations are so important, could it be that patients being administered the real drug don't react to it fully due to the expectation they might be on the placebo?
Addendum: Steve Waldman (of Interfluidity and Naked Capitalism) posts in the comments:
@llimllib on twitter - Bill Mill - posted a cite (in response to a tweet on this post) that seems like a nice confirmation of your conjecture. Almost perfect.Wow.
@llimllib on twitter - Bill Mill - posted a cite (in response to a tweet on this post) that seems like a nice confirmation of your conjecture. Almost perfect.
I think it's a misconception that the placebo effect is a magical psychosomatic response to positive thinking. My understanding is that it's a bit of a myth and its roots are more banal: people who are ill often get better over time; if they don't, their bodies at least have an ability to adapt and ignore symptoms. If one compares the outcomes between a sugar pill sample and a left-untreated sample, the placebo effect drops out. This is a good 'un: http://www.ncbi.nlm.nih.gov/pubmed/11372012
I think the nocebo story still holds true though. In cases of recovery that are merely symptom adaptation, drawing attention to potentially worse symptoms could counteract the body's natural ability to adapt to discomfort. Upshot: in double-blind placebo trials I wouldn't expect an underestimation of effectiveness of the treatment group. And I can't think of an occasion where a double-blind nocebo trial would be used?