The Anecdotal Fallacy
Alias: The Volvo Fallacy1
Last year, tens of millions of people bought life insurance for scheduled flights of airlines in the United States. Not one of those insured passengers died in a crash…. [T]ravel insurance…is now purchased by half of American leisure travelers―a fivefold increase since 2001, according to the United States Travel Insurance Association. As a purely economic investment, some of this insurance can be dubious, particularly the flight insurance policies. … Because calamities are so vivid and easily brought to mind, we tend to overestimate their probability when we intuitively judge what will happen….3
The Anecdotal Fallacy is committed when a recent memory, a striking anecdote, or a news story of an unusual event leads one to overestimate the probability of that type of event, especially when one has access to better evidence. In other words, the mistake is to allow the emotional effects of a vivid memory or story to outweigh stronger evidence, such as statistics, on the frequency of such events.
- According to psychologists, people tend to judge the probabilities of types of event by using the "availability", or "ease of representation", rule of thumb:
So, it's the "availability" to memory or imagination that gives this rule of thumb its name. It's not a very memorable or descriptive name for a simple idea: if we can easily remember an event of a certain type or imagine it happening, then we tend to think it more likely than if we cannot do so.
Like all rules of thumb, the ease of remembering or imagining"representing"a type of event is evidence of degree of likelihood in ordinary circumstances. Instances of a type of event which we frequently experience will be easily remembered, so that that type will be correctly judged to be likely. Moreover, if one has a hard time remembering an event of a given sort, then it is probably rare and unlikely.
If there are many ways that a kind of event can come about, then it will be easy to imagine and also likely to happen. Whereas, if we cannot even imagine it, then there may be almost no way for it to occur. However, unusual events do happen, and if they happen to us or someone we know then we tend to overestimate their likeliness.
You may have had the experience of seeing an accident on the road, then slowing down and driving more carefully afterwards. Of course, it's a good idea to slow down in the immediate vicinity of an accident scene, since there may be wreckage on the road. Also, it's possible that the accident took place where it did because the area is an unusually dangerous one. However, the vivid memory of the accident and your heightened caution may have lasted after you were well away from the accident scene.
The experience of seeing one may make accidents more vivid in your memory, thus making them seem more probable. However, the probability of getting in an accident in one place is not increased by seeing one in another.5
- Relying on memories or imagination when judging the probability of events may have worked well for our ancestors, but in the modern world we are exposed to vivid vicarious experiences through the communications media. Unfortunately, common events make for uninteresting stories, and we're more interested in the out-of-the-ordinary.
There's an old saying: "When a dog bites a man that is not news, but when a man bites a dog that is news." In other words, relatively common events are not newsworthy; it's the unusual that makes news. So, the news media frequently expose us to uncommon events as "news", and we acquire a mistaken impression of how common such events are.
As a result of this fallacy, many people are fearful of highly unlikely events, such as terrorism, shark attacks, and strangers kidnapping their children. Such exaggerated fears can lead people to take unnecessary and even harmful actions, such as buying expensive flight insurance, or driving instead of flying, which is statistically safer.
We often fear most those things that are least likely to happen, and fail to take precautions against more probable risks. In this way, the Anecdotal Fallacy may well have done more damage to the human race than any other mistake in our thinking.6
- Richard E. Nisbett, Eugene Borgida, Rick Crandall & Harvey Reed, "Popular Induction: Information is Not Necessarily Informative", in Judgment Under Uncertainty: Heuristics and Biases, Daniel Kahneman, Paul Slovic & Amos Tversky, editors, (1985), pp. 112-113. The source of the "Volvo fallacy" alias. The name comes from the following thought experiment:
Let us suppose that you wish to buy a new car and have decided that on grounds of economy and longevity you want to purchase one of those solid, stalwart, middle class Swedish cars―either a Volvo or a Saab. As a prudent and sensible buyer, you go to Consumer Reports, which informs you that the consensus of their experts is that the Volvo is mechanically superior, and the consensus of the readership is that the Volvo has the better repair record. Armed with this information, you decide to go and strike a bargain with the Volvo dealer before the week is out. In the interim, however, you go to a cocktail party where you announce this intention to an acquaintance. He reacts with disbelief and alarm: "A Volvo! You've got to be kidding. My brother-in-law had a Volvo. First, that fancy fuel injection computer thing went out. 250 bucks. Next he started having trouble with the rear end. Had to replace it. Then the transmission and the clutch. Finally sold it in three years for junk."
Would you still buy a Volvo?
I prefer the name "Anecdotal Fallacy" to "Volvo Fallacy", despite the fact that the latter is the older name for this mistake. The problem with the elder name is that it connects to the mistake involved only through the story above. For those unfamiliar with or who do not remember the story of the brother-in-law's Volvo, the original name will not call this type of error to mind. In contrast, "Anecdotal Fallacy", while not perfect, should suggest the nature of the mistake committed, namely, treating a vivid anecdote as stronger evidence than dry statistics.
- This fallacy is a subfallacy of Biased Sample because, if the Anecdotal Fallacy is based on a single anecdote, then it is a hasty generalization. No matter how emotionally compelling a particular incident is, it is just one data point. If, instead, it is based on more than one anecdote, the set of such stories is unlikely to be representative of the class generalized about. This is especially true if the anecdotes are based on news stories, since journalists tend to write about unusually extreme events. What we read or hear about from the news media are the best or worst case scenarios.
- John Tierney, "Appeasing the Gods, With Insurance", The New York Times, 5/6/2008.
- Daniel Kahneman, Paul Slovic & Amos Tversky (editors), Judgment Under Uncertainty: Heuristics and Biases (Cambridge University Press, 1982), Part IV.
- Thanks to Stephen Rowe for a criticism of this passage which led me to revise it.
- With the possible exception of The Gambler's Fallacy.