Introduction

Errors in judgement are often traceable to pitfalls of human reasoning. One pitfall is the availability heuristic, defined as a tendency to judge the likelihood of a condition by the ease at which examples spring to mind. This intuition is often a great approximation but can be sometimes mistaken because of fallible memories. People, for example, may mistakenly believe drowning causes fewer deaths than fires in the USA (actual deaths in 2017: drowning=3709 vs fires=2812)1 because they cannot easily recall many news stories about drowning. Calm water is boring to imagine whereas bright flames are dramatic images vividly recalled and frequently popularised. In turn, people can underestimate the risks lurking in lakes or rivers and neglect basic safety strategies. This may be an example where the availability heuristic could cause a fatal mistake.

Diagnostic errors can also stem from the availability heuristic and contribute to serious mistakes in patient care. One pregnant patient diagnosed with Zika virus infection, for example, may provoke wide public attention, lead to excessive viral testing of pregnant women and result in underestimating more likely contributors to maternal morbidity including domestic violence, mental illness and traffic crashes.2 Of course, a formal analysis of diagnostic possibilities for every case would demand substantial effort and, itself, does not guarantee a correct diagnosis. In addition, the availability heuristic often leads to the right diagnosis by providing a quick and easy guess.3 This means the availability heuristic will have enduring appeal in medical …