Anecdotal evidence. An oxymoron? Or a valid approach to understanding data?
The problem is there are different kinds of anecdotes, used for different purposes, but the purpose of anecdotes is rarely if ever defined explicitly. Anecdotes are used for one purpose by one speaker/writer but interpreted in a different context by the listener/reader. People love anecdotes, especially if the anecdotes are about them or their beliefs. Anecdotes are how patients transmit the particulars of their disease to their health care providers. The medical history, as taken from the patient, is an extended anecdote, from which the particulars of the disease have to be extracted. Anecdotes are how physicians explain disease and treatments. Anecdotes are a tool with which teachers instruct their students. Anecdotes are how CAM proponents validate their particular system, and how skeptics invalidate them.
Anecdotes are useful tools for presenting yourself and your ideas. The convention season is over and is was striking how the candidates attempted to win over voters with anecdotes about their lives rather than the particulars of their policies. Using variations of ‘anecdote’ as a pubmed search term yields little of substance. The predominant theme on medline is to contrast anecdotes with evidence, always to the detriment of anecdotes. Anecdotes have power to influence far greater than evidence.
On The Skeptics Guide to the Universe #165 there was an interview with Ben Goldacre, who noted that there was the popular misbelief that the MMR vaccine was a cause of autism. The belief waned not when the voluminous data on the safety and lack of association with autism and the MMR was released, but when it was discovered that the primary proponent of the MMR/autism link received large sums of money to testify about that MMR/autism link. It was the anecdote about his conflict of interest that invalidated the idea, not the science.