Availability Bias
Availability Bias is the tendency to judge the likelihood of an event based on how easily examples of it come to mind, rather than on objective probabilities, causing investors to overweight vivid or recent market events.
The availability heuristic was introduced by Kahneman and Tversky in their 1973 paper and describes how the brain estimates probability through mental ease rather than statistical rigor. Events that are easy to recall — because they are recent, emotionally intense, widely covered by media, or personally experienced — feel more probable than they actually are. Events that are historically infrequent but have not occurred recently feel less probable than base rates suggest.
In financial markets, availability bias shapes risk perception in systematic ways. After a major crash, investors overestimate the probability of another imminent crash. The 2008 financial crisis remained cognitively 'available' to an entire generation of investors for over a decade, contributing to chronically high equity risk premiums and slower recovery in retail participation than historical patterns would have predicted. The term 'recency bias' is often used interchangeably, though availability is the broader concept.
Availability bias also inflates the perceived risk of dramatic but statistically rare events. Plane crashes generate extensive coverage, making air travel feel dangerous despite its safety record; the same dynamic applies to high-profile corporate frauds. After Enron and WorldCom, corporate accounting fraud felt ubiquitous, prompting risk-aversion that extended well beyond companies with any plausible accounting concerns.
On the upside, availability bias can inflate perceived opportunity. During the early days of generative AI in 2023, vivid narratives about transformative disruption made the probability of specific AI companies achieving dominance seem far higher than sober base-rate analysis would support. Capital flooded toward names associated with AI regardless of competitive moats or valuation.
Correction requires deliberate reference to base rates: historical frequency distributions of crashes, defaults, or sector transformations compiled over decades rather than recent headlines.