One of the questions I find most curious is "why do people continue to do or use things that patently don't work?" There are, of course, societal issues at work when a person is choosing how to respond to events; however, a naive view would be that as experience accumulates, more effective responses will be acquired.

This is clearly not true in the case of alternative medicine. Many alternative treatments, from homeopathy to a variety of herbal remedies, have been shown to be ineffective—yet they persist, and, in many cases, have become big business. To understand why failure can be successful, a group of researchers have put together a mathematical model that accounts for how treatment decisions spread. This has allowed them to show that ineffective treatments are often more successful in society than efficacious alternatives.

The model is based on the extremely simple idea that, if I am sick, I will choose some action to try and make myself better. This action may or may not be efficacious, but regardless of that, I will have, in effect, demonstrated that treatment to my associates. Of course, I will likely recover from illness whether or not the treatment works. So, independent of the impact of the treatment, some of my associates may choose to use it, since they're aware that I did and am now well.

There are other details considered in the model, as well. For instance, treatment may be abandoned, illnesses can either be single events (e.g., chicken pox) or recurring events, and I may continue to demonstrate a treatment after recovery. Stir this in with a numerical value for the efficacy of the treatment—a scale that encompasses treatments that actually hurt recovery through those that are ineffective and those that are effective—and one can see how a given treatment regime can spread through social learning.

The most ironic finding is that a very effective treatment has only a very short demonstration period, so it's very unlikely to spread unless the user continues to demonstrate it after they recover. In fact, if treatment abandonment rates are sufficiently low, harmful practices are the most effective in spreading through a population.

Once recurring illnesses are taken into account, the ground begins to shift towards more efficacious treatments. However, all of the data shows a broad local maxima of spread located near an efficacy of zero (e.g., ineffective treatment), meaning that an effective treatment actually needs to be pretty good before it can spread.

There are, of course, other reasons for refusing to use an effective treatment. For instance, Africa, long exploited by the west, has an understandable mistrust of western practices. But this is certainly not true in the west, where, for the most part, effective treatment regimes don't have cultural baggage associated with them. Nevertheless, large portions of society have turned to various forms of snake oil for treatment, which this model goes some way towards explaining.

It also helps me understand why the meme of vaccine damage has spread. There are literally no demonstrators for the effectiveness of vaccination, making social learning difficult.

PloS One, 2009, DOI: 10.1371/journal.pone.0005192