3. Always remember that correlation does not entail causation. Believe it or not, if we look across the population of the United States, shoe size is highly correlated with general knowledge; people with bigger shoes tend to know more history and more geography than people with smaller shoes. But that doesn’t mean buying bigger shoes will make you smarter, or even that having big feet makes you smart. This correlation, like so many others, seems more important than it really is because we have a natural tendency to confuse correlation with causation. The correlation I described is real, but the natural inference — that one factor must be causing the other — doesn’t follow. In this example, the reason that the correlation holds is that the people with the littlest feet (and tiniest shoes) are our planet’s newest visitors: infants and toddlers, human beings too young to have yet taken their first history class. We learn as we grow, but that doesn’t mean that growing (per se) makes us learn.[55]
4. Never forget the size of your sample. From medicine to baseball statistics, people often fail to take into account the amount of data they’ve used in drawing their conclusions. Any single event may be random, but recurrence of the same pattern over and again is less likely to be an accident. Mathematically speaking, the bigger the sample, the more reliable the estimate. That’s why, on average, a poll of 2,000 people is a lot more reliable than a poll of 200 people, and seeing someone bat .400 (successfully getting a hit in 40 percent of their tries) over 10 baseball games doesn’t mean nearly as much as seeing them bat .400 over a 162-game season.
As obvious as this fact is, it’s easy to forget. The person who first formalized this notion, known as the law of large numbers, thought it was so obvious that “even the stupidest man knows [it] by some instinct of nature,” yet people routinely ignore it. We can’t help but search for “explanations” of patterns in our data, even in small samples (say, a handful of baseball games or a single day’s stock market results) that may well reflect nothing more than random chance. Boomer hit .400 in the last ten games because “he’s seeing the ball real well,” never because (statistically speaking) a .300 hitter is likely to occasionally look like a .400 hitter for a few days. Stock market analysts do the same thing, tying every day’s market moves to some particular fact of the news. “The market went up today because Acme Federated reported unexpectedly high fourth-quarter results.” When was the last time you heard any analyst say “Actually, today’s rise in the market was probably nothing more than a random fluctuation”?
Happily, psychologist Richard Nisbett has shown that ordinary folks can be taught to be more sensitive to the law of large numbers in less than half an hour.
5. Anticipate your own impulsivity and pre-commit. Odysseus tied himself to a mast to resist the temptations of the Sirens; we would all do well to learn from him. Compare, for example, the groceries we might choose a week in advance, with a well-rested stomach, to the junk we buy in the store when we are hungry. If we commit ourselves in advance to purchasing only what we’ve decided on in advance, we come home with a more healthful basket of groceries. “Christmas Clubs,” which tie up money all year long for holiday shopping, are completely irrational from the perspective of an economist — why earmark money when liquidity is power? — but become completely sensible once we acknowledge our evolved limitations. Temptation is greatest when we can see it, so we are often better off in plans for the future than in impulses of the moment. The wise person acts accordingly.
6. Don’t just set goals. Make contingency plans. It’s often almost impossible for people to stick to vague goals like “I intend to lose weight” or “I plan to finish this article before the deadline.” And simply making a goal more specific (“I plan to lose six pounds”) is not enough. But research by the psychologist Peter Gollwitzer shows that by transforming goals into specific contingency plans — of the form “if X, then Y” (for example, “If I see French fries, then I will avoid them”) — we can markedly increase the chance of success.
A recognition of our klugey nature can help explain why our late-evolved deliberative reasoning, grafted onto a reflexive, ancestral system, has limited access to the brain’s steering wheel; instead, almost everything has to pass through the older ancestral, reflexive system. Specific contingency plans offer a way of working around that limitation by converting abstract goals into a format {if-then, basic to all reflexes) that our ancestral systems can understand. To the extent that we can speak the language of our older system, we increase our chances of achieving our goals.
7. Whenever possible, don’t make important decisions when you are tired or have other things on your mind. Thinking while tired (or distracted) is not so different from driving while drinking. As we get tired, we rely more on our reflexive system, less on deliberative reasoning; ditto as we get distracted. One study, for example, showed that a healthful-minded consumer who is given a choice between a fruit salad and a chocolate cake becomes more likely to choose the cake when forced to remember a seven-digit number. If we want to reason by emotion alone, fine, but if we prefer rationality, it is important to create “winning conditions” — and that means, for important decisions, adequate rest and full concentration.
8. Always weigh benefits against costs. Sounds obvious, but it is not something that comes naturally to the human mind. People tend to find themselves in either a “prevention” frame of mind, emphasizing the costs of their actions (if I don’t go, I’ll waste the money I spent on concert tickets), or a “promotion” frame of mind, emphasizing the benefits (It’ll be fun! Who cares if I’ll be late for work in the morning?). Sound judgment obviously requires weighing both costs and benefits, but unless we are vigilant, our temperament and mood often stand in the way.
Pay special attention, by the way, to what some economists call “opportunity costs”; whenever you make an investment, financial or otherwise, ponder what else you might be doing instead. If you’re doing one thing, you can’t do another — a fact that we often forget. Say, for example, that people are trying to decide whether it makes sense to invest $100 million in public funds in a baseball stadium. That $100 million may well bring some benefits, but few people evaluate such projects in the context of what else that money might do, what opportunities (such as paying down the debt to reduce future interest payments or building three new elementary schools) must be foresworn in order to make that stadium happen. Because such costs don’t come with a readily visible price tag, we often ignore them. On a personal level, taking opportunity costs into account means realizing that whenever we make a choice to do something, such as watch television, we are using time that could be spent in other ways, like cooking a nice meal or taking a bike ride with our kids.
9. Imagine that your decisions may be spot-checked. Research has shown that people who believe that they will have to justify their answers are less biased than people who don’t. When we expect to be held accountable for our decisions, we tend to invest more cognitive effort and make correspondingly more sophisticated decisions, analyzing information in more detail.
For that matter (and no, I’m not making this up) office workers are more likely to pay for coffee from a communal coffee machine if the coffee machine is positioned under a poster featuring a pair of eyes — which somehow makes people feel that they are accountable — than under a poster that has a picture of flowers.
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Pop quiz: should we study the dictionary to make ourselves smarter? Maybe, maybe not: lots of websites promising to build vocabulary tell us that “people with bigger vocabularies are more successful,” but is it the vocabulary that makes them successful, or some third factor, like intelligence or dedication, that leads to both success and a large vocabulary?