Sunday, December 26, 2010


Follow-up on placebos

I wanted to do a follow-up to Friday’s post about a ridiculously flawed study of the effect of placebos. I have two follow-up points.

Point 1: The study is not blinded, but that is not a problem, as I see it. There are two types of blinding used in studies:

  1. Blinding relative to the subjects: the subjects don’t know which group they’re in (and sometimes don’t know specifically what’s being studied). This reduces the influence of the subjects’ expectations and biases on the results.
  2. Blinding relative to the researchers: the researchers don’t know which group a given subject is in. This reduces effects that the researchers’ behaviour toward the subjects will have on the results.

For this study, the whole point was not to blind it to the subjects. And since the subjects are either being treated or not, there’s nothing to blind relative to the researchers, either. The problem with the study isn’t the lack of blinding, but the bias that the instructions to the subjects provides.

Point 2: I see a reasonable way to evaluate what these researchers want to evaluate, which fixes the bias problem — or, more accurately, which makes that bias part of the study itself. It involves what I’ll call half blinding relative to the researchers.

Get, say, 300 subjects, and divide them into three groups of 100. Group A gets no treatment, just as one group got in the existing study. Groups B and C each get identical bottles labelled PLACEBO. Each bottle contains identical pills. Each bottle contains an instruction sheet that only the subjects see, and each subject is told to read his sheet and not to discuss with anyone what it says.

The instruction sheets for group B would say, This bottle contains placebo pills made of an inert substance, like sugar pills, that have been shown in clinical studies to produce significant improvement in IBS symptoms through mind-body self-healing processes.

The instruction sheets for group C would say, This bottle contains placebo pills made of an inert substance, like sugar pills, that have no effect whatsoever. They will not affect your symptoms in any way.

Now, if groups B and C have similar results, we can legitimately say that placebos have their effect even when the subjects know they’re getting them. But if, as I suspect, group C has results comparable to those of group A, then what we’ve shown is that telling people the placebos are effective is the same as not calling them placebos — setting up the expectation of effectiveness is what gives the results.

If you want to call that mind-body self-healing processes, that’s fine with me. Well, almost fine: it’s not healing; it’s symptom relief. That your mind can help you feel better is no surprise. But it’s not going to heal your cancer, repair your liver damage, or kill viruses. Unless, perhaps, someone can show, with a properly designed study, that it can.

No comments: