Is Jack Reacher a Bayesian?

We’ve covered why Jack Reacher would be a good financial advisor. In A Wanted Man, Reacher once again proves his mettle. To set the scene, we’ve got two bad guys (we think) on the run from our two heroes (we think). It’s rural Iowa and Reacher and Hero Two need to figure out which way the troublemakers fled.

Reacher, a man of action, says they have to act fast.

“Now? They could be in a million different places.”

“So it’s time to gamble. Before I get taken off this thing. Or supervised. One or the other is sure to happen first thing in the morning. That’s what maximum effort means. So suppose the two guys are still on the road?”

“But which road? There are a million roads.”

“Suppose they stayed on the Interstate?”

“Would they?”

“They’re probably not local. They’re probably running home right now, which could be a big distance.”

“In which direction?”

“Either one.”

“You said they might be traveling separately.”

“It’s a possibility, but a small one. Statistics show most paired perpetrators stick together after the commission of a serious crime. Human nature. They don’t necessarily trust each other to deal with the aftermath.”


“We find them to be a useful guide.”

Part-of-what-makes the Reacher books so popular is his fists the size of supermarket chickens. Part is his modern day sleuthing. Reacher is curious and he notices things. If he took the stairs at 22B Baker Street—two at a time, of course—he’d know how many there were. Part of the reason is Reacher’s knowledge of base rates.

Julia Galef explained Bayesian thinking this ways: “It’s important to pay attention to these snowflakes of evidence that maybe weigh very little on their own but if you pay attention to them and notice how they accumulate, their collective weight becomes enough to break a tree branch.”

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