Barrowman on Placebos

Wednesday, October 05, 2011

Statistician Nick Barrowman takes a look at the burgeoning area of research into the placebo effect and questions its very premise. (HT: John Cook)

Suppose a clinical trial randomizes 100 patients to receive an experimental drug in the form of pills and an equal number of patients to receive identical pills except that they contain no active ingredient, that is, placebo. The results of the trial are as follows: 60 of the patients who received the experimental drug improved, compared to 30 of the patients who received the placebo. The drug clearly works better than the placebo.[1] But 30% of the patients who received the placebo did get better. There seems to be a placebo effect, right?

Wrong. The results from this trial provide no information about whether or not there is a placebo effect. To determine whether there is a placebo effect you would need compare the outcomes of patients who received placebo with the outcomes of patients who received no treatment. And not surprisingly, trials with a no-treatment arm are quite rare.
Barrowman further quotes from a meta-study of 130 trials in which some patients received placebos and some no treatment:
We found little evidence in general that placebos had powerful clinical effects. Although placebos had no significant effects on objective or binary outcomes, they had possible small benefits in studies with continuous subjective outcomes and for the treatment of pain.
Following this quote is an interesting look at a trial of an asthma medication in which placebos and non-treatment were compared with the medication, and two measures of improvement were employed: the patients' own ratings of improvement and a measurement of expiratory volume. A placebo effect showed up in the first measure, but not in the second.

Barrowman goes on to consider why the placebo effect has been getting so much attention lately, and, finally, the kind of rhetorical disadvantage skeptics will find themselves facing when they raise objections:
Curiously, however, in more scientific circles recent developments in neurobiology have also encouraged interest in the placebo effect. Advances in understanding of how the brain works have lead to research efforts to understand the mechanism of action of the placebo effect. This is more than a little odd, given the fairly sparse evidence for such an effect! An article in Wired Magazine asserts that "The fact that taking a faux drug can powerfully improve some people's health -- the so-called placebo effect -- has long been considered an embarrassment to the serious practice of pharmacology." Note that the article takes for granted "the fact" that the placebo effect works.

Indeed, the term "the placebo effect" itself is part of the problem. By labeling it as an effect, we lend it credence. Arguing against the placebo effect seems to put one at an immediate disadvantage. Hasn't everyone heard of the placebo effect? How could anyone deny such an established fact? [bold added, minor format edits]
I myself ran into (and blogged) the Wired article Barrowman links above some time ago. I recall finding attractive the idea that "mind hacks" could cure or mitigate some illnesses, at the time. Unfortunately, attractiveness, plausibility, and consistency with some widely-accepted belief are not the same thing as truth. (This is not to say that this tactic could never work; only that, if it can, the situations in which it can are probably much less common than one might wish.)

-- CAV


Andrew said...

Not really much to add, besides that I found your post exceptional and well worth the read. Thanks for posting it. The placebo effect (or maybe I should say "effect") has fascinated me for years. I guess I haven't done my due diligence on investigating the so-called "studies" done on it.

Gus Van Horn said...


I wouldn't necessarily use scare quotes when speaking of the placebo effect, but I'd be much more guarded about how I use the term.

Andrew said...

Yea I meant them more as a so-called quote then a scary quote but I get what you mean

Gus Van Horn said...

No worries. More or less the same thing.