Innumeracy: Your Brain Can’t Math and How That’s Being Used Against You

Welcome the second in our new series, Mondays Musings with Matt. Matt has authored many of our most popular posts (i.e. Fattest People in Paleo, Your Non-Cooperative Spouse, and What It Feels Like to Lose 200lbs, among many) not to mention is also the chef. His first installment, Logical Fallacies, was an awesome start!  I hope you’ll find this series to be thought provoking and help you find your own path to health. -Stacy

You have ten fingers and ten toes. This makes you an expert at conceiving of numbers between zero and ten, and pretty good at eleven through twenty. Back in hunter-gatherer times, that set of numbers was very helpful. You can easily conceive how many people are around the fire, what food you have gathered that day, how many spears you have left or how many children you have with you. Indeed, early family groups probably numbered around a dozen, and we were comfortable with considering that many people.

As humans began to form larger groups, it necessitated us to start considering larger numbers. Tribes began to include many different family groups forming a large body. It turns out that your brain is able to handle about 100 to 250, usually averaging to about 150, different relationships which happens to also be the average size of hunter-gatherer tribes. This is a concept called Dunbar’s Number. So while you may have 500 Facebook friends, you’re probably only interacting with less than 150 on any kind of regular basis. (And I should pause here to say that we’re talking averages here. You, yourself may be a special social butterfly type that has a high limit. Or you may be a hermit like me and really prefer about 100 relationships.) Even before we had a concept of this being a limit, we were already organizing ourselves into this grouping. Military history shows that organization falls around this number as the size of a unit, from a Roman century to a modern company. Early villages also tended to sustain at this population.

Of course, the substantial growth in human population led to larger groupings, by necessity. Today, we have mega cities like New York, Tokyo, Shanghai and Mexico City that have populations in the tens of millions. No one could possibly conceive of 20 million people as individuals. Such large numbers are no longer seen as “things” by our brain. They’ve become abstract concepts to us that just happen to have actual real world values.

We can’t math that high.

This is a very significant problem for us. We now deal with numbers that are so high that we cannot handle them as concepts. It’s almost as if your brain divides numbers into three categories: under 20 is small, under 150 is big, every thing else is just too high to count. That’s why when a relatively small tragedy occurs, we really focus on it. Thirteen died in Columbine, 20 died in Sandy Hook, 52 died in the 7/7 bombings, for example. But we have a harder time conceiving of and focusing on the larger tragedies, such as the 200,000 in Darfur, Sudan or the 500,000 in Rwanda. This is the oft quoted adage, “The death of one man is a tragedy, the death of millions is a statistic.”

But it doesn’t have to be events that make us susceptible to this. We’re bad at figuring out what risks there are. If I were to ask you what the most common cause of death was in the US, you’d probably easily pick out heart disease, cancer, and lung disease. But you’re probably unclear how much they account for. Over half of all deaths are due to one of those three causes. Not only that, but you’re about 4.5 times more likely to die of heart disease or cancer than in an accident. But what about homicide and suicide, big dramatic incidents that we hear about so often? Well, you’re 50 times more likely to die of heart disease than you are of homicide, and you’re 2.5 times more likely to die of suicide than homicide. If you’re confused by those multipliers, by the way, that was intentional; we’re also really bad at comparing numbers, too.

Relative vs. Absolute

If you hear in the news that, for an absurd example, that people who consume a pound of grapes per day are 50% less likely to develop arm cancer than people who do not, you may run out to the store and start buying grapes. But what exactly is being said here? There is a difference between relative risk and absolute risk. If 10 percent of all people in the United States were destined to get arm cancer, then a 50 percent reduction would mean that 15 million people were going to avoid arm cancer! Hallelujah! That’s amazing. But what if the actual number of people who would get arm cancer was more around 1000. Then that means we’ve only prevented 500 cases. Five hundred represents .00167% of the US population. Because you were never likely to contract arm cancer to begin with, your absolute risk has changed hardly at all. This is often how advertising and marketing portrays statistics in a way that tricks you!

Money, Money, Mon-Ay!

And then there’s money. Once we start talking big dollar amounts, we can’t conceive of the sums at all anymore. For a quick example, I want you to think of all of your wealth and put a dollar amount on it. Now consider what would happen to you if lost 90% of it. You’d probably be on the streets. But if you were Bill Gates, you would, alas, tragically only be as wealthy as Elon Musk, founder of PayPal, Tesla Motors, Space-X and one of the coolest dudes on the planet. Ah! But what if Elon Musk lost 90%? Well, he’d still have 800 million and be well within the top 1% wealthiest people on the planet.

Another thing to consider is government spending. Because we hear about billions and millions of dollars being thrown around by governments, we’ve stopped considering these large sums since they’re too big for our minds. But it’s important to consider their relative values in order to understand their contexts. For example, people often lament the spending of foreign aid. Yes, the US tends to spend around $30 billion in foreign aid, a large number in any scale. But, when placed in context of the entire US budget, it’s only 1.4%. My favorite example of this is the NASA budget. When surveyed, people tend to estimate the budget of NASA as being about 24% of the US budget. In fact, the budget for NASA is about .5%. But once you tell someone 10 billion dollars is going to NASA, it makes a much bigger impression than .5%.

Math & Paleo

So how does this relate to paleo? Understanding numbers is very important when we’re making health choices. There is no perfect way to live, after all, and everything is about trade offs. What is the impact of spending 50% more money on organic produce as it relates to longevity and health? Is the impact a 10% improvement to absolute risk of cancer? Is it a 10% decrease to your quality of life since you will subsequently have less disposable income? What is the actual risk of eating that brownie? And what about policy decisions. We spend an extremely large amount of money on health in this country. Would we spend less if we shifted farm subsidies from soy, corn, and wheat to programs that encourages production of fruits and vegetables? Or would people eat less overall and be negatively impacted by malnutrition if the price of grain products increased?

The fact remains that worrying about the little things that have little chance of harming you will definitely have a negative impact on your health, your stress and your sense of well being. I don’t worry about dying by violence and I never have. My risk of that is low here in my suburban US neighborhood, and that risk is on par with my chance of dying by accidentally ingesting a poison. What I can and should be worrying about is reducing risk factors for heart disease, stroke, lung disease, infectious disease, and cancer. I do that by eating an overall healthy diet, exercising frequently, following the advice of medical science and not engaging in excessively unhealthy behaviors like smoking or doing hard drugs. Once those things are in place in your life, you’re on the right track to a healthy, long life. All the rest of it will impact you only minimally and it’s up to each of us to figure out the hard math.

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