The Availability Heuristic in Practice

We all use mental models (heuristics, rules of thumb) across a host of simple and complex problems. They often work; they sometimes don’t. You shouldn’t (and can’t) avoid having and using them, but you should be aware of them (and their limitations).

The Influence of the Availability Heuristic on Physicians in the Emergency Department” is a cute little paper demonstrating recency bias in real-life practice:

Heuristics, or rules of thumb, are hypothesized to influence the care physicians deliver. One such heuristic is the availability heuristic, under which assessments of an event’s likelihood are affected by how easily the event comes to mind. We examined whether the availability heuristic influences physician testing in a common, high-risk clinical scenario: assessing patients with shortness of breath for the risk of pulmonary embolism.

The sample included 7,370 emergency physicians who had 416,720 patient visits for shortness of breath. The mean rate of pulmonary embolism testing was 9.0%. For physicians who had a recent patient visit with a pulmonary embolism diagnosis, their rate of pulmonary embolism testing for subsequent patients increased by 1.4 percentage points (95% confidence interval 0.42 to 2.34) in the 10 days after, which is approximately 15% relative to the mean rate of pulmonary embolism testing. We failed to find statistically significant changes in rates of pulmonary embolism testing in the subsequent 50 days following these first 10 days.

Of course, one of the biggest components of the availability heuristic in real life isn’t just how recent the event is (though that’s what’s measurable in this sort of dataset). It’s anything that makes certain events easier to recall. This is, for example, why some of our mistakes or surprise diagnoses can have an outside impact on our practice. We remember that unexpected PE we didn’t see coming more than the many more common examples of the negative CTA.

(Further reading availability bias: Farnam Street.)

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