• Robb G. Best

The Proportionality Problem

Decision making: it’s what humans do. Estimates are that the average adult makes 35,000 decisions a day. Of those daily decisions, 226 involve food choice. The fact that you’re reading this suggests that, for the most part, your decisions have allowed you to stay above room temperature, and live your life.

Still: are you the kind of person who tends to make good decisions? How well have you navigated through the maze of everyday choice? Can you point to at least a couple of dead ends from your past? In all honesty, if you had the chance, how many do-overs would you take?

Given that our brains tend to remember our successes while confining our mistakes to the outer reaches of our minds, many of us probably think our decision-making is pretty good.

The truth might not be so comforting. After all, there’s a reason Las Vegas can support over 62,000 hotel rooms on the strip alone. According to PBS, $6 billion are lost every year in Vegas.

Gambling aside, why might our decision apparatus betray us more often then we’d like to admit? It’s basically a math issue--a problem of false equivalency. When presented with a binary choice, the human brain displays an interesting flaw: it does a poor job with proportionality.

Imagine two individuals debating an idea. Subject A cites the testimony of 10,000 scientists and extensive research to argue that the earth is round. Subject B asserts that the Flat World Society and its five card-carrying members can prove the earth is as flat as a pancake. After all, Subject B points out, from 30,000 feet away in an airplane, the earth appears flat.

You’d think this would be a no-brainer, an easy rebuke of the Flat World folks. But think again. When presented with two different views, research shows it’s the two individuals themselves we tend to size up, shrugging at vast amounts of evidence or bodies of supporting views. (Especially when the evidence runs counter to our current belief.)

Our brains set up a simple binary exercise: this person against that person, or this idea against that. You might have an army of experts who can offer real verifiable proof, but your opponent only needs to hit an emotional chord and the listener’s brain levels up the playing field, the weight of evidence be damned.

How has this flaw survived? One theory is that assigning proportional weight doesn’t necessarily have an evolutionary advantage. Imagine your ancient ancestor encountering a poisonous snake. Whether they chanced upon three or thirty deadly serpents, it didn’t really matter. It only takes a bite from one snake to die. In this scenario, quantitative attributes become less important. One snake might as well be thirty.

Without the ability to weigh proportionality easily, we become easy prey for weak and unsupported claims—provided the advocate has good presentation skills. PT Barnum is purported to have said, “There is a sucker born every minute.” Although it’s unlikely Barnum actually said that, still if we’re going to put false words in his mouth, we might as well make a quick revision: Maybe not a sucker, but someone who frequently has a problem with rudimentary math.

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