Wired has an excellent article on how the placebo effect is increasing in drug trials and how drug companies are trying to understand why. It’s an intriguing article but it conflates two distinct concepts of ‘placebo’ that need to be separated to fully understand the effect.
The term ‘placebo effect’ is used to refer to two things in the medical literature. The first is a statistical concept and it refers to the improvement in patients given an inactive treatment in a drug trial in comparison to those given the actual drug. The second is a psychological concept and it refers to improvement due to expectancy and belief.
If you’re not sure how these are different, you may be surprised to learn that you don’t need a mind to demonstrate the placebo effect – in fact, even rocks can show it.
Let’s say an oil tanker has sunk, the local beach is covered in oil, and you want to compare how effective two cleaning products are – the first, liquid soap, our active treatment, and the second water, our placebo.
So we randomly assign oily stones to a bucket of soapy water or to a bucket of water. It turns out that while stones in the soap condition become less oily, so do stones in the placebo condition, although, perhaps, the effect is weaker. Oil breaks down on its own, water movement disperses it, oxygenation happens. There’s a whole bunch of stuff which means our placebo ‘treats’ the stones.
Statistically we have a placebo effect, because in a trial anything which causes improvement not to do with the active treatment is chalked up to the placebo effect.
In humans, similar effects are at work. Most illnesses improve on their own, when we catch anything at its worst typically it will return to its normal state (an effect known as regression to the mean), people change their behaviour to become more healthy when they’re ill, and so on. None of these are to do with expectancy or beliefs about taking a pill.
But here’s the other thing. Because the statistical concept of placebo is drawn from the study data, the study itself has an effect.
For example, the strength of the placebo effect is measured relative to the active treatment. The Wired article says that placebo is getting stronger, which is another way of saying that the difference between placebo and the drug is getting smaller.
It turns out that the more rigorous the study the less strong the drug effect is, or, in other words, the stronger the placebo effect.
For example, we know that better designed and higher quality studies show smaller drug effects. This includes things as simple as randomisation. If your method for randomly allocating people to groups is more susceptible to bias, it’s more likely to produced biased results. Better randomisation improves the placebo effect, again, nothing to do with expectancy or belief.
So one reason why the placebo effect might be increasing is that studies are just more rigorous these days.
Of course, on top of all of these things, individual psychology plays a part as it adds improvement, and anything which leads to improvement gets captured by the statistical placebo effect.
However, the lab-based studies which investigate placebo look almost exclusively at the psychological placebo effect. They examine the effects of beliefs and expectations but usually carefully control the presence of the unpleasant thing, like pain, so it doesn’t naturally improve and you can’t change your behaviour like you would in real life.
You can’t explain the statistical placebo effect just with psychology. It’s part of it, but not the whole story.
So when I read the article which said that drug companies are busily doing lab studies to understand why the placebo effect is increasing I became a bit suspicious.
The first thing you’d do is look at how your studies have been run, not look at the psychology of belief. Drug companies undoubtedly know this. They’re masters of drug trial sleight-of-hand and know research methods inside out.
The article touches on a likely explanation – marketing. They would like to influence your beliefs so the drug works better for you, because once it’s on the market, it’s the customers’ experience that brings them back for more.
In an industry where genuinely new drugs are rare and most are just no-better copies of rival medications, your beliefs could make all the difference.
Link to Wired on the increasing placebo effect.
Link to previous Mind Hacks post on the psychology of placebo.