What is the Availability Heuristic?
Tversky and Kahneman’s (1973) availability heuristic argues that people sometimes judge the frequency of events in the world by the ease with which examples come to mind. When forced to make a decision, we rely on what is brought to mind quickly, which is a useful mental shortcut. However, this undermines our ability to accurately judge frequency and magnitude.
We make decisions based on what we remember. We assume our memories are a representative sample of reality, and discount events that are outside of our immediate recollection. If we can quickly think of multiple examples of something (police shootings, car accidents) we will believe that is quite common.
However, our memory has limitations. When something comes in a vivid narrative it increases the ease of recall. Ironically, we then believe rare events to be more likely than they actually are exactly because they are unique and stand out.
What we remember is especially influenced in the modern world by what issues and events are covered in the media, especially in news stories. In Thinking Fast and Slow, Kahneman writes:
People tend to assess the relative importance of issues by the ease with which they are retrieved from memory—and this is largely determined by the extent of coverage in the media.
The news has the effect of making some events, often rare ones, more visible by giving them heavy media coverage. This makes it much easier for us to recall than less widely covered, but possibly more frequent events.
Why does it matter
We often lack the time or resources to investigate an issue in depth when engaging in decision making. The availability heuristic is therefore a useful way to quickly arrive at conclusions. In many cases this is based on the principle of “if I can remember it easily, It must be important”. However, if we rely on faulty estimates of the probability of an event, our perceptions of risk and error may be skewed and lead us to focus on the wrong risks or ignore the important ones.
A commonly cited example of the availability heuristic is Kahneman & Tversky’s experiment that asked people to recall words that begin with the letter K versus those that have K as their third letter. Because we can much more easily recall words such as kitchen, kangaroo and kale, we ignore the fact that there are actually about twice as many words with K in third place (e.g. ask).
Another oft-cited example is the case where after watching a number of television programs about shark attacks, you believe the likelihood of a shark attack is more common than in reality. You then refuse to swim in the ocean on vacation. An interesting knock-on effect is that after a shark attack the number of deaths from drowning decrease for a few years. Our reaction to reports of shark attacks is greater than to those of drownings because the former is remembered more vividly.
Karlsson, Loewenstein, and Ariely (2008) showed that people are more likely to purchase insurance to protect themselves after a natural disaster they have just experienced than they are to purchase insurance on this type of disaster before it happens.
Doctors that have diagnosed two cases of a serious disease arw likely to see it in the next patient if they have similar symptoms, even if the patient only has a much milder illness. This could lead to improper treatment.
In the world of finance, investors will make judgements of stocks based on having heard about them recently in the news, and find that they subsequently underperform in later years.(Tversky & Kahneman, 1974).
Lottery companies are employing the availability heuristic when they remind us of recent winners. We subsequently overestimate our own likelihood of winning and divert money towards the purchase of lottery tickets.
Tversky, A., & Kahneman, D. (1974). Judgment under uncertainty: Heuristics and biases. Science (New Series), 185, 1124-1131.
Tversky, A., & Kahneman, D. (1973). Availability: A heuristic for judging frequency and probability. Cognitive Psychology, 5, 207–232