A difficult situation that rationalists can find themselves in is when discussing bogus treatments such as acupuncture, homeopathy, and such like is that there will always be someone who will say something like, "well I tried it and it worked", which is followed by an anecdotal story and the almost obligatory comment, "explain that".
How does this arise?
People may be introduced to an alternative treatment or remedy by advertising, but it's more commonly a recommendation by friends, family, acquaintances or even Internet communities.
They will therefore try out the remedy with enthusiasm and have a positive expectation of it based on other people's reported success stories. If the problem that they are using the remedy for is cured or improves then they are convinced that the remedy works. They have seen it with their own eyes and once they are convinced by their own personal experience, no logical, coherent argument or explanation will change their mind.
Why is personal experience not acceptable?
Relying on personal experience is a "try it and see" approach which is akin to open testing (see: testing). It is wide open to the confounding factors which can lead to false conclusions. There are many ways that an ineffective treatment can appear to work. Assigning the cure of self-limiting illness to the bogus therapy probably being the most common reason that convinces people that the alternative remedy has worked.
The big problem with relying on personal experience is that it is very convincing to the individual concerned even when the conclusion formed is wrong. People are aware that they can be deceived by others; they are not generally aware that they can be deceived by themselves.
This is not the end of the story however. Once a person's mind is made up by a personal experience, they make a second major mistake. The fallacy that is confirmation.
People now "know" that the treatment works and will accept any evidence that confirms their belief. Contrary evidence, including the results of quality clinical trials, is simply ignored and the unquestioning belief continues.
This is all a result of believing in the infallibility of our own personal experience.
The consequence of this is that the myth that alternative treatments are effective is spread by the power of personal testimony.
People who promote alternative remedies this way rarely change their mind or back down. Their mistakes should be pointed out however, so that others can avoid making the same mistake.
The bottom line is: personal testimony (or anecdotes) does not count as good evidence. Anyone who has been given a recommendation for a treatment should not be swayed by anecdotes, even though the person may genuinely be trying to help, and should check out the clinical evidence to support the proposed remedy. If there is no evidence then the remedy is bogus and the person has mistakenly fallen for the fallacies explained above.
"it is human nature to empathise with stories about individuals while remaining unperturbed by statistics, whatever their implications"
Nick Ross - Healthwatch