The Availability Heuristic

Another common heuristic is the availability heuristic. Here, one forms a judgement on the basis of what readily comes to mind. Many of our judgements rely on frequency estimates (e.g., what are the chances of dying from a particular cause, or if a friend recommends a movie, how often have they been right in the past). To make such judgements we must draw upon our memory of instances of that event. So, if we remember something easily (i.e., easily think of an instance), we think it must be more frequent. But the ease with which memories are generated can be affected by factors other than frequency. For example, imageability, recency, and unusualness are three factors that can influence or recollection of memories. Question 11 provides a demonstration of how this heuristic can lead to a fallacy:

Question 11

Version A

In a sample of 2000 words taken from an English novel, estimate the number of words of 4 letters or more that end in “ing”.

Version B

In a sample of 2000 words taken from an English novel, estimate the number of words of 4 letters or more that end in “g”.

Question

How did you respond on this question? Would your answer on the other question be higher or lower? Let’s examine the data:

Reveal graph

People tend to give a larger number for Version A compared to Version B, even though all words ending in “ing” also end in “g”. This inaccuracy comes from the fact that one can think of more words when a larger part of it is given (not to mention that “ing” is also easily identified as a common suffix), so the fragment is thought to be more common than the letter.

Brainstorm

What are some real-life examples of reliance on the availability heuristic?

For example, what is the deadliest animal on earth (to humans)?

Example

The answer is, in fact, the mosquito! You may have chosen a more “flashy” animal, given that information about mosquito deaths does not as readily come to mind (compared to say, shark deaths). One could argue that the representativeness heuristic is also at play here given that people may not even have considered mosquitoes as part of the category “animal”.

A few other examples:

From Sunday Morning Breakfast Cereal.

Even experts are not immune from potential cognitive biases from relying on the availability heuristic – for example, doctors’ estimates of the likelihood of dying as a result of certain diseases are highly correlated with the number of articles published about that disease (Christensen-Szanlaski et al, 1983).