Mar 11 2008
Placebos are inactive treatments used in clinical trials as a comparison for the active treatment being studied. This is necessary because there is a host of artifacts and effects that create the appearance of a response to a treatment above and beyond any real physiological response – collectively called “the” placebo effect. To further illustrate how squirrelly the placebo effect can be, Waber et. al. recently published a study (you may need a subscription to access this link – here is a link to a NYTimes article discussing the study) in which they found that more expensive placebos had a greater effect on pain reduction than less expensive placebos.
The researchers looked at 82 subjects who were receiving a placebo they were told was a pain reliever and their pain tolerance was assessed using small electrical shocks (a standard procedure). Half of the subjects were told the placebo was a medication that cost $2.50 per pill and the other that it cost $0.10 per pill – 85.4% of the subjects getting the expensive placebo experienced pain reduction, while only 61% of the cheap placebo group experienced pain reduction.
While many news outlets reports these results as surprising, they actually make perfect sense. The study authors interpreted the findings as indicative of a well-known marketing effect – that of quality expectations. We expect higher quality from more expensive products, or lower quality from cheap products. Therefore those subjects who were told their placebo cost $2.50 per pill had higher expectations of efficacy, perhaps resulting in the release of more pain-fighting endorphins. The authors speculate, reasonably, that this effect may explain why many people believe that expensive brand name drugs are more effective than their cheaper, but chemically identical, generic alternatives.
However, while I think this explanation is plausible and probably a factor, it reflects the common assumption that the placebo effect is chiefly a mind-over-matter phenomenon, while downplaying or ignoring the many other factors that make up the placebo effect. One such factor is the purely psychological effect known as investment justification. This results from our tendency to justify to ourselves investments of time, energy, money, or other resources by convincing ourselves that the investment was justified by a proportional benefit. So if we sink time, money, and hope into a treatment we want to believe it was worth it, therefore we convince ourselves that we are better, even if there has not been any real physical improvement.
Of course this, like any psychological factor, is not absolute. There are also many ways to reduce the cognitive dissonance resulting from believing in a treatment that does not work other than just self-deception that it did work. For example we could come to the belief that the treatment was worth a try, that the chance of benefit was worth the investment. Or that the investment was justified because of the hope that it brought, if nothing else. Or we could conclude that we were deceived by those offering the treatment or making the claims for it, and therefore we can blame our loss of investment on someone else and see ourselves as a victim.
This is a very interesting study that further illuminates the nature of the placebo effect. I would like to see it replicated with more subjects, while also exploring other aspects of this effect – for example would it also be seen for outcomes other than pain. But also the lesson we should take away from studies such as this is that the placebo effect is actually a complex array of multiple effects. Some of those effects are psychological, which themselves may be complex and subtle and yet have a profound effect on the apparent response to a treatment. Placebo control is a critical part of our medical science technology, and therefore we are wise to understand the nature of the various placebo effects as much as possible.
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