Availability bias in investing: why vivid recent events distort portfolio decisions

Availability bias is the tendency to judge the probability of an event by how easily examples of it come to mind. Events that are recent, dramatic, or personally experienced feel more likely than they actually are, because the ease of mental retrieval is mistaken for a signal about frequency. In investing, availability bias leads to overestimating the probability of crashes after crashes, overestimating the continuation of bull markets at their peaks, and systematically chasing the investments that have been most visible—which are often those that have already performed.

What availability bias is

Tversky and Kahneman (1973) demonstrated the availability heuristic in a series of experiments showing that people judge the frequency of a class of events by the ease with which instances come to mind. Vivid, emotionally charged, or recent events are more cognitively available than routine, abstract, or distant ones—and this availability is mistakenly used as a proxy for probability. Asked whether more words begin with the letter 'k' or have 'k' as their third letter, most people choose the former, because words beginning with 'k' are easier to retrieve—even though English words are more likely to have 'k' in the third position. The same mechanism operates in financial judgements.

In investing, the most cognitively available events are those that have been reported most extensively in financial media. A crash that dominated news coverage for months creates a highly available mental representation of extreme losses. A persistent, quiet bull market that rarely makes headlines is less available, even if it represents the dominant historical pattern. The asymmetry in how dramatic events are covered and remembered means that investors' subjective probability estimates for extreme market events are systematically distorted upward relative to actual historical frequencies.

How it manifests in investing

After a major market crash—2000–2002, 2008–2009, 2020—many investors remain underinvested in equities for years, expecting a repeat. The crash is highly available; the subsequent recovery, which happened more quietly, is less so. This pattern produces a systematic tendency to underallocate to equities during recoveries and to remain cautious long after the rational case for caution has passed. Research on investor flows into and out of equity funds has consistently shown that retail investors reduce equity exposure after large drawdowns—at or near market troughs—and increase it after sustained rallies—near market peaks.

Barber and Odean (2008) found that individual investors are net buyers of attention-grabbing stocks—stocks in the news, stocks that have experienced extreme recent returns in either direction, and stocks with unusually high trading volume. This pattern is consistent with availability bias: stocks that are cognitively available become the candidates for active purchase decisions, even when the attention is driven by noise rather than information. The result is a systematic tendency to concentrate in assets that have been most visible recently, which are disproportionately those at elevated valuations.

FOMO—the fear of missing out—is a manifestation of availability bias at market peaks. When an asset class has recently delivered dramatic returns and its performance is widely discussed, the gains feel highly certain to continue, because examples of recent success are cognitively available while historical examples of mean reversion are not. Investors who have not participated in the rally experience this as an urgent pressure to buy before being left behind. The pattern is well-documented in technology stocks in 1999–2000, residential real estate in 2005–2006, and cryptocurrency in late 2017 and again in 2021.

The cost

The cost of availability bias is concentrated in poor timing decisions. Dalbar's annual Quantitative Analysis of Investor Behaviour—a long-running study of actual investor returns in US equity funds—has consistently found that individual investors earn substantially lower returns than the funds they invest in, due to buying after strong performance and selling after drawdowns. The average gap between fund return and investor return has historically been 2–4 percentage points per year over rolling twenty-year periods, primarily attributable to availability-driven timing decisions.

What helps

The structural antidote to availability bias is an allocation process that is anchored to systematic signals rather than to the salience of recent events. A rules-based investment strategy that determines allocation weights based on momentum, value, or carry metrics—applied consistently regardless of what is currently in the news—does not allow the vividness of recent market events to distort the weighting process. The strategy holds less of a declining asset not because its recent fall makes further declines feel likely, but because the momentum signal has turned negative; it holds more of a rising asset not because recent gains make further gains feel certain, but because the signal is positive. The news creates the availability; the system ignores the availability.

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