Medical treatments with no direct effect, such as homeopathy, are surprisingly popular. But how does a good reputation of such treatments spread and persist? Researchers from the Centre for the Study of Cultural Evolution in Stockholm believe that they have identified the mechanism.
They argue that most medical treatments result in a range of outcomes: some people improve while others deteriorate. If the people who improve are more inclined to tell others about their experiences than the people who deteriorate, ineffective or even harmful treatments would maintain a good reputation.
They conducted a fascinating study to test the hypothesis that positive outcomes are overrepresented in online medical product reviews, examined if this reputational distortion is large enough to bias people’s decisions, and explored the implications of this bias for the cultural evolution of medical treatments.
The researchers compared outcomes of weight loss treatments and fertility treatments as evidenced in clinical trials to outcomes reported in 1901 reviews on Amazon. Subsequently, in a series of experiments, they evaluated people’s choice of weight loss diet after reading different reviews. Finally, a mathematical model was used to examine if this bias could result in less effective treatments having a better reputation than more effective treatments.
The results of these investigations confirmed the hypothesis that people with better outcomes are more inclined to write reviews. After 6 months on the diet, 93% of online reviewers reported a weight loss of 10 kg or more, while just 27% of clinical trial participants experienced this level of weight change. A similar positive distortion was found in fertility treatment reviews. In a series of experiments, the researchers demonstrated that people are more inclined to begin a diet that was backed by many positive reviews, than a diet with reviews that are representative of the diet’s true effect. A mathematical model of medical cultural evolution suggested that the size of the positive distortion critically depends on the shape of the outcome distribution.
The authors concluded that online reviews overestimate the benefits of medical treatments, probably because people with negative outcomes are less inclined to tell others about their experiences. This bias can enable ineffective medical treatments to maintain a good reputation.
To me, this seems eminently plausible; but there are, of course, other reasons why bogus treatments survive or even thrive – and they may vary in their importance to the overall effect from treatment to treatment. As so often in health care, things are complex and there are multiple factors that contribute to a phenomenon.