The availability heuristic is a cognitive bias which describes our tendency to use information that comes to mind quickly when making decisions. If we think of something quickly (i.e., it’s more available to our memory), we assume it’s a more frequent and more probable event. If we have a harder time thinking of something (less available), we assume it’s less likely to happen.
In their seminal 1973 research on the availability heuristic, Tversky & Kahneman asked participants which was more common: words that start with letter K or words that have the letter K as their third letter. Since it is much easier to think of words that start with K (kitchen, kangaroo, kale) than words that have K as their third letter (ask, cake, bike), most participants chose starts with K. However, there are actually about twice as many words that have K as their third letter. The bias caused by the availability heuristic led to the wrong decision.
The available bias explains why people overestimate the risk of certain uncommon events (plane crashes, shark attacks, and terrorist attacks) while underestimating the risk of more common ones (car crashes, cancer). The former often receive highly sensationalized media coverage, making them easier to remember, while the latter don’t get the same level of media attention. As a result, many people are more worried about travelling by plane than by car even though it’s been calculated that driving is 65 times riskier than flying.
A similar situation happens in annual performance appraisals. Managers usually base their evaluations more on the prior three months than the nine months before then because it’s easier to remember the details of what happened recently (i.e., it’s more available). Managers also give more weight to unusual one-off behavior, such as a serious mistake or notable success, than the normal state. Research has shown we are more likely to remember these incidents based on how vivid they are than based on how common they are. The availability bias can cause us to incorrectly characterize others.
In short, we tend to overestimate the likelihood of uncommon events and underestimate the likelihood of common events. As a result, the availability heuristic negatively impacts decision making because “memories that are easily recalled are frequently insufficient for figuring out how likely things are to happen again in the future”. Remember, the key to success isn’t predicting the future but rather getting the odds right.
The bias caused by the availability heuristic reminds us that just because we can vividly remember something doesn’t mean it’s likely to happen again.