Anecdotal evidence has several definitions, which usually relate to how certain types of evidence cannot be used to logically conclude something. We see examples of this type of evidence all the time in commercials. A person tells us how their breath feels fresher after using a certain brand of toothpaste, or people testify to the clearing of their acne as a result of special products. This type of evidence is often used in place of clinical or scientific evidence, and may completely ignore research or harder evidence that points to an opposite conclusion.
Types of anecdotal evidence include claiming non-factual information based on the experiences of a few people, stories that would seem to contradict factual information, and word of mouth recommendations. This type of information isn’t always poorly intended or untrue, and we base a lot of decisions on anecdotes. For instance, you might want to find the best dry cleaner in town and ask a few friends to recommend someone. You usually don’t have time to perform true scientific testing on this by looking at a range of data.
We take other recommendations from non-experts all of the time. We may base our decisions about which doctors to see, who should baby-sit our kids, what travel agency we ought to use, or where we should stay on vacation solely or at least partly on advice. This advice usually doesn’t come from people who are qualified to give an expert opinion on the matter.
Where anecdotal evidence gets very problematic, though, is when people make decisions that may affect their health or well-being based solely on it. For instance, there are many herbal medications and alternative medical theories and treatments that people decide to use largely based on anecdote. Now sometimes a preponderance of this evidence may suggest that there’s a good reason to try different things, but unfortunately many of these alternative treatments and therapies are not just there for the health and happiness of humans. People who offer them are profit motivated too.
If you look at most diet supplement websites for instance, you’ll probably find tons of testimonials that are truly anecdotal evidence. These testimonials seem to lend credence to the idea that each diet treatment will be tremendously effective. Yet we know they are not. When people are desperate to lose weight though, they may cling to these testimonials and information presented as “evidence,” and occasionally risk their health by taking things that are not safe and haven’t been proven safe. At minimum they waste money on products that simply don’t work.
Another definition of anecdotal evidence refers strictly to legal matters. When someone gives testimony that can’t be proven by its nature, and is thus in doubt, it is called anecdotal or hearsay. Some witnesses may be banned from giving evidence that is anecdotal in nature. It doesn’t mean that their testimony is untruthful, but it does mean that there is no way to verify this testimony.