Anecdotal evidence
Anecdotal evidence is a term used for testimonial evidence based on an anecdote. The evidence may be right or wrong, though the implied support is lacking.
Example: Smoking doesn't cause lung cancer, "My grandmother lived to 95, smoked constantly, and didn't die of lung cancer." The data proves than not all smokers die of lung cancer, but fails to see the data that 90 percent of the lung cancer cases are smokers. This is very close to suppression of data, but differs, because all the data from that type of study will show the same thing. All smokers living to 95 don't die of lung cancer, some do. Suppression of data would be "No smokers studied living to 90+ died of lung cancer."
What the data does prove is that not all smokers die of lung cancer, and can live to a "ripe old age".
The conclusion in this case is false or lacking support. The lack of support is usually because the evidence given doesn't stand up to additional evidence from a wider scientific study.
Example: People wearing top hats live longer, was supported by a great deal of anecdotal evidence. People that wear top hats are usually richer, therefore can afford better food, shelter, sanity, and medical resources. A wider study including people's income identified the false claim.
It commonly is also erroneously used as a term to indicate (pseudo-)scientific evidence based on single episodes ("personal anecdotes"), instead of verifiable statistics.
It is incorrect to use the term that way, the data given is correct and collected reliably. The above description would better be termed false data, or unreliable data. There is no reason for the data to revolve around single episodes. The narrowness of a study can be the downfall.
Anecdotal evidence may confuse correlation with causation.
Examples
- "I have smoked all my life and I am perfectly healthy." Not all smokers develop lung cancer, but 90 percent of the lung cancer cases are smokers.
- "John never drinks wine, and he had a stroke." There are other causes of stroke than excessive alcohol.
- "Today is the coldest day in the century, and people talk about global warming!" Single point temperature measurements do not show a global trend. The evidence supporting global warming incorporates that piece of data. There is a great sum of data showing predominantly warmer temperatures, than the few that are colder, including that one.
External Links
- "Anectodal Evidence" from a course in Critical thinking at Santa Rosa Junior College.
- "Anecdotal Evidence".