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How to Be a Better Guesstimater

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man_thinking_numbersIs the murder rate in the U.S. increasing or decreasing? What percentage of teen girls will give birth this year? What percentage of Americans are Christian or Muslim? What percentage are immigrants?

If you guess wrong, you’re not alone. A new global survey, building on work in the UK last year for the Royal Statistical Society, finds that most people in the countries surveyed were wildly wrong. For instance, Americans guess wrong on each of the following questions:

• What Percentage of Girls Age 15-19 Give Birth Each Year? (Avg. guess: 24 percent; Actual: 3 percent)

• What Percentage of People Are Muslim? (Avg. guess: 15 percent; Actual: 1 percent)

• What Percentage of People Are Christian? (Avg. guess: 56 percent; Actual: 78 percent)

• What Percentage of People Are Immigrants? (Avg. guess: 32 percent; Actual: 13 percent)

• What Percentage of People Voted in the Last Major Election? (Avg. guess: 57 percent; Actual: 67 percent)

• What Percentage of People Are Unemployed and Looking For Work? (Avg. guess: 32 percent; Actual: 6 percent)

While these examples may seem relatively trivial, they highlight that when it comes to numbers that shape policy and politics, many Americans are extremely confused. Ideally, before making a decision about how to vote or stressing about the latest health threat, we’d research the numbers to develop an informed decision. But the number of issues we face each day often prevents us from doing more than making a “best guess.”

Fortunately, there are ways we can hone our skills at guessing and estimation — guesstimation — that will help us minimize our innumeracy. Here are a few tips for making better guesses about numbers related to politics, policy, and demographics:

Choose (and know) your reference points — For policy purposes, one essential reference point is the population of the U.S., which is currently 316 million. But for purposes of guesstimation, 315 is close enough and easier to use in mental calculations.

That’s a big number, so you’ll also want to have a few other ways to gauge large numbers of people. For example, it may be helpful to know that California has 38 million people (round up to 40), Texas has 26 million (round down to 25), or New York City has 8 million.

Keep in mind these numbers are only useful if they make sense to you. If you’ve never been to New York City you may not be able to grasp just how big the city is or how crowded it can be. Choose references, such as your city or state, that will help you in your guesstimation.

Translate into both percentages and fractions — A lot of guesstimation problems occur when we use percentages without translating them into their equivalent fraction.

From elementary school math you learned that 20 percent is “1 out of 5”, 25 percent is “1 out of 4”, 33 percent is “1 out of 3”, etc. These types of fractions are particularly useful when thinking about populations, and can prevent us from making some obvious mistakes.

For instance, a Gallup poll found that U.S. adults, on average, estimate that 25 percent of Americans are gay or lesbian, and young adults estimated about 30 percent (the real answer is about 2 percent). Do these people really think that 1 out of 4 people in the U.S. (about 79 million people (315 / 4 = 78.7)) or even on 1 out of every 4 people they know are homosexual? Probably not. They just didn’t think about how the percentage translates into more commonsensical terms.

Think outside your circles — The esteemed movie critic Pauline Kael famously said, after the 1972 Presidential election, “I live in a rather special world. I only know one person who voted for Nixon. Where [Nixon voters] are I don’t know. They’re outside my ken.” Prior to that election, Kael probably would have done a poor job of guesstimating how many people would vote for Nixon. We tend to make comparisons based on the groups we know or come in contact with, which can cause us to over/under-estimate the size of those groups.

For instance, if you work in a crisis pregnancy center, it may seem reasonable to assume 1 out of 4 young teen girls are getting pregnants. Similarly, if you live in an urban area, such as Chicago, you are likely to encounter more immigrants and overestimate their size relative to the general population. Always consider how your own experience may bias your guess.

taylorswiftAsk, “Is that a big number? — During the height of the recent ebola panic, a clever meme spread around the Internet that noted, “More Americans have been dumped by Taylor Swift than have died from ebola.” You don’t even need to know how many men Ms. Swift has dated (about a dozen) to understand the comparison. The meme works because it provides a guesstimation-style response to the question “Is the number of people who have died from ebola in America a large number?”

Of course, what is considered a large number is relative, so we need to make the appropriate comparisons. If one American out of 315 million has died from ebola, that is not a big number. But we might also want to compare it to a similar circumstance, such as the flu virus. Flu-associated deaths range from a low of about 3,000 to a high of about 49,000 people. While there may be sensible reasons to by concerned about the spread of ebola, we are currently much more likely to die from the flu.

Consider the precision of the question — Finally, we need to take into account the question or claim under consideration. For instance, President Obama recently said that, “It is estimated that 1 in 5 women on college campuses has been sexually assaulted during their time there — 1 in 5.” What is surprising is that if that statistic is true, then Obama — and ever other sensible adult — should be warning women to completely avoid college campuses, just as they would advise against walking down a dark, unfamiliar alley in a crime-ridden part of a city.

But the two questions we have to ask upon hearing that claim are “It it true?” and “How do they define sexual assault?” The answer to the first part is clearly “no.” The second part if a bit trickier. In the source Obama quotes, “sexual assault” includes both “rubbing up against you in a sexual way, even if it is over your clothes while you were drunk and unable to consent” and violent sexual penetration. If you’re a young woman, you may want to know how much of each category is included in such a statistic before deciding whether to apply for college.


While guesstimation shouldn’t take the place of becoming informed about actual facts, it can be a helpful way for us to process the deluge of stats and figures that wash over us on a daily basis. And since we’re already going to make such guesses anyway, we might as well develop a process to do it more effectively.

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Joe Carter Joe Carter is a Senior Editor at the Acton Institute. Joe also serves as an editor at the The Gospel Coalition, a communications specialist for the Ethics and Religious Liberty Commission of the Southern Baptist Convention, and as an adjunct professor of journalism at Patrick Henry College. He is the editor of the NIV Lifehacks Bible and co-author of How to Argue like Jesus: Learning Persuasion from History's Greatest Communicator (Crossway).