Heuristics are mental shortcuts that allow you navigate the world quickly and efficiently. Many heuristics are very useful, because they allow you to understand a situation and respond to it without processing every piece of information in detail. They are ways of getting an answer quickly, that usually work, but in some cases lose you some accuracy. You can think of spelling rules as heuristics: “i before e, except after c” is a common one that is taught at school (at least, I learned it in the UK!), and works for most words. But not all. “Eight”, “efficient”, “protein”, “glacier” all break the rule, so if you applied the heuristic in all cases, you would make some mistakes. In this way, a heuristic is different to a hard-and-fast rule that is always followed (of which there aren't many in the English language).

The availability heuristic describes the finding that your reasoning and decisions are influenced by the ease of bringing something to mind. It works as follows. Let’s say I asked students at my university whether the UMass Lowell campus is safe or not, on a scale from 1 = extremely dangerous, to 5 = extremely safe. If, as we sometimes do, the students had just received an emergency notification about an armed robbery on the campus, they would likely give the campus a lower safety rating than if they had received that same notification a month ago, and it was less readily available in their memory.

However, in reality the safety of a campus is not dependent on whether there was an incident today or last week, but instead on a much richer set of data: the average number of incidents, divided by the number of people who live/visit the campus, and compared to other areas or campuses. But that is far too complicated for us to really consider unless we are crime statisticians. Instead, we tend to automatically and effortlessly classify the campus into “dangerous” (I just read about an armed robbery today!), “less dangerous” (I think there was something about an armed robbery a while back but I don’t really remember), and “safe” (I can’t remember reading anything about a crime recently).

Here is a quite different example of the availability heuristic. Participants in two groups were asked to either recall a handful of childhood memories, or many childhood memories from each age in their childhood in response to word prompts (1). For example, participants might have been asked to recall a memory from age 7 that related to the keyword "apple". Afterwards, both groups were asked whether there were some large chunks of their childhood that they couldn’t recall.

Now, recalling a lot of memories is harder than recalling just just a few. As a result of doing the more difficult task, participants who had to report a lot of childhood memories were more likely to agree with the statement that there were large chunks of their childhood memory that they couldn’t recall, than participants who only had to recall a few memories. Remember that participants were randomly assigned to these conditions, so there was no reason to think that those in the "lots of memories" condition would actually have poorer childhood memories. I always joke that I will do this to my students before end-of-semester teaching evaluations: make them try to list MANY ways in which I could improve the class. Since it will be so hard for them to think of SO MANY different improvements, may they will come away thinking that the class was great!

If you're interested in learning more about the availability heuristic, you can listen to this podcast episode by David Dylan Thomas.

References:

(1) Winkielman, P., Schwarz, N., & Belli, R. F. (1998). The role of ease of retrieval and attribution in memory judgments: Judging your memory as worse despite recalling more events. Psychological Science, 9, 124-126.