A positive pregnancy test
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The power of the complement

A tactic to handle probabilities is also a surprising trick to make sense of dubious statistics and combat fear of missing out

Koen Smets
7 min readMay 31, 2024

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Probability is a tricky, unintuitive concept, that has a capacity to trip up even people who might generally be expected to know better. Imagine an urn with 10 balls in it, nine worthless wooden ones and a golden one. If you are allowed to draw one ball, you have a 1-in-10 chance of finding the valuable one. If you draw two balls from the urn, you double your chance to 2-in-10, if you pick nine, you have a 90% chance of picking the golden ball and if you pick all ten, then, well, you are certain to get the prize. Probabilities simply add together, don’t they?

A chance mistake

Well, not quite. Andrew Huberman, a neuroscientist at Stanford University and host of the Huberman Lab podcast, explains in one of the episodes why couples trying to conceive should wait at least six months before starting to worry that something may be amiss: “ For women under 30, because the probability of getting pregnant on any one attempt is 20%, if it doesn’t occur the first time she should simply repeat at least five and probably six times, before deciding that there is something going on, because 20 times five is 100, so we’re talking about

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Koen Smets

Accidental behavioural economist in search of wisdom. Uses insights from (behavioural) economics in organization development. On Twitter as @koenfucius