I first dipped my toes in the waters (no pun intended) of behavioral psychology and the adaptation of those principles to medical decision making in 2008, with my first national presentation on the subject of “cognitive error” – the mistakes and misjudgments made by both medical professionals and patients when heuristics, biases, and other “fast” thinking strategies go awry.

Since then, I’ve used the illustration of a shark attack to explain the Availability Bias (Kahneman and Tversky) – in a nutshell, the mental illusion that memorable events are more likely to occur than their statistical rarity predicts. This availability can be due to multiple factors, some with their own labels, such as how recently a similar event occurred (‘recency bias’), how novel or vivid an anecdote is, highly publicized a similar event has been, whether the event happened to us personally, whether it was associated with a strong negative emotion, an so on.

I’ve said to numerous audiences that although shark attacks are vivid. emotional, and make incredible headlines (and are therefore memorable), more people are killed each year by extremely mundane causes, including simple falls, bicycling accidents, and catching the flu. (Yes, you have a 1 in 63 chance of dying from the flu vs 1 in 3,700,000 chance of being killed by a shark during your lifetime.) Therefore, rationally speaking, the imagery from Shark Week or Jaws should not stop us from enjoying the waves.

Similarly, having had a strongly emotionally charged and recent adverse medical outcome due to a rare confluence of factors should not cause us to deviate from our usual best practices going forward. We should continue according to the standard of care and best evidence, knowing that such rarities are indeed rare. But as most every doctor will confirm, we’ve all been “burned” by something, and now we “always do XYZ” or “never do ABC” because of that isolated and rare incident.

This Saturday, I’m heading to the coast for a family vacation. Yep, the same North Carolina beaches that boast a wild streak of no less than 8 (!!) shark attacks in recent weeks, the highest number in over 80 years. What is happening? Are we under siege?

According to some experts, these shark attacks are “extraordinary,” represent “incredible odds” and a “perfect storm“. Hypotheses abound – is it climate change, the economy (seriously), a prehistoric megalodon forcing average sharks closer to shore?

Map of NC shark attacks in 2015

But then I am reminded that the human brain has a skewed idea of what “randomness” looks like – a point made in “Fooled by Randomness” (Nassim Nicholas Taleb), “Nudge” (Thaler and Sunstein) and others, based on scientific studies (Gilovich, Tverksy, Vallone) replicated many times over.

If we flip a coin and it comes up “tails” several times in a row, that doesn’t seem random. If we’re playing Roulette, and red comes up ten times in a row, we think that somehow influences the next outcome (red is hot! or we’re due for black!).


So I wonder – could these shark attacks simply represent randomness over time and space, even though they’ve been characterized as a feeding frenzy? In two weeks, I’ll have the opportunity to ask Drs. Thaler and Kahneman in person at BX2015 in London.

Even if due to mere chance, I still probably cannot use the shark attack illustration anymore, at least among local audiences.

And come this Saturday, should I go in the water? What would you do?

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