Human Minds Vs. Large Numbers, Round 2

Meet Bob. He’s in his late fifties, a quiet guy, wears rimless spectacles, and likes to read poetry. Do you think Bob is a classics professor or a truck driver?


If you answered classics professor, you’re with the vast majority of people asked this question. Quiet, spectacles, poetry reader, all of it pretty well fits the common image of a classics professor and not so much our image of a truck driver. But while there are approximately 7500, maybe at a stretch 10000 classics professors in the US, that number is blown out of the water by a couple orders of magnitude when compared with how many truck drivers there are. The American Trucking Association’s website says there are 3,500,000 truck drivers in the country, making it much, much more likely that Bob is a quiet, poetry-reading truck driver. He may not fit the NASCAR-loving truck driver stereotype, but it’s still more likely.

It’s much more likely, but that’s not the way we think. Humans look for patterns, make categories, and form stereotypes in order to make sense of the world. If our early ancestors heard a scream, they did not sit down to calculate the probability that their friend Og had trod on a surprise thorn bush versus the probability that Og had just been snack for a saber-toothed tiger. No, they used their learned pattern of scream = bad and got the hell out of there.

Because while we could calculate the probability that our friend was in a tiger’s mouth, it would take a lot of brain power, and time. Instead, humans have evolved to subconsciously use rules of thumb to shortcut through all the mental effort, or as psychologists like to call it, cognitive demand. The technical name for the mental shortcuts we use is heuristics, and they dominate our decision making more than we realize.

When people are trying to decide whether Bob is a professor or a truck driver, they use the representativeness heuristic. People subconsciously compare Bob’s characteristics to their idea of what a truck driver is, as opposed to what they imagine a classics professor is like. The stereotypes offer a quick way to decide which is a better match with Bob, without resorting to complex mental calculations. If the question was framed as “is it more likely that Bob is a classics professor or a truck driver?” it may be easier for people to realize that due to sheer probability, the best guess is that Bob is a truck diver. But the heuristics we use are designed to avoid such mental math and effort, thus leading most people to say Bob is a classics professor.

There are other types of heuristics, and while they’re generally useful for everyday decision making, there are some cases where they fail. Many, many more people are afraid of flying than driving, while airplane crashes resulted in 52 total fatalities in the US in 2009 and driving claimed 10.8 million lives in 2009. More than 200,000 times more people died in cars than in planes, but it’s way more common to meet someone afraid of flying than of driving. Why the fear?

This is where the availability heuristic fails us. Instead of turning to statistics and probabilities to consider safety, we think about all the examples of accidents we know about. When plane crashes do happen, they tend to be large-scale tragedies. These accidents receive a lot of media attention, because they are both tragic and rare, coverage that sticks in many people’s minds. Car accidents, on the other hand, happen every day. Because they’re common, they’re not news, and few people hear about them and their frequency. When evaluating all the available anecdotal evidence about the frequency of crashes on planes versus cars, terrible plane crash memories are what dominate. This shortcut skips the mental effort of figuring out the actual probability of crashing, but isn’t at all accurate due to the unrepresentative pool of occurrences the decision is based on. With more airport security to keep us safe comes more stress associated with flying. More stress pushes more people to choose to drive to Grandma’s house, unfortunately resulting in more traffic fatalities.

Being conscious of the usefulness and traps of heuristics also pays for anyone buying a car. The first number mentioned will determine the rest of negotiations; suggest a number, and our next guesses or offers will be influenced by that number. Cognitive psychologists like to ask about the height of the Empire State Building to demonstrate this, except some people get asked if the tower is higher or lower than 5,000 feet and by how much, and other people are asked if it is higher or lower than 1,000 feet. People’s guesses are consistently higher when the researchers casually mention 5,000 feet, even though that is nearly the length of a mile and the tower is actually 1,454 feet. The mentioned number anchors and influences all of our future estimates. Knowing about the anchoring heuristic can make anyone into a much smarter bargainer.

Shortcuts usually serve us well; we get someplace faster and with less effort. But mental shortcuts aren’t perfect or completely reliable. We don’t realize we’re using heuristics, but being aware of them helps catch their weaknesses. In the end, for a big decision it’s better to just do the math. It takes effort, but it’s way more accurate.


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