10 Well-Known Facts That Aren't Actually True

Half of all marriages don't end in divorce, and men don't think about sex every seven seconds. Sometimes, what we think we know is dead wrong.

1. Half of all marriages end in divorce.

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Often cited and too rarely scrutinized, this figure is a simple comparison of the number of divorces in a given year with the number of marriages. But since those two figures represent two very different groups of people, the 50% number doesn't say much about the chance your uncle's wedding next week will eventually go sour. It doesn't even make mathematical sense — it's conceivable, if unlikely, that there could be more divorces in a year than marriages, resulting in a divorce "rate" that's greater than 100%.

The true number is far fuzzier. Researchers sometimes look at the proportion of people who were ever married and then later divorced for a more meaningful stat, and this figure is below 50% for all age groups.

2. Men think about sex every seven seconds.

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In 2011, researchers at Ohio State University found that college-age men thought about sex about 19 times a day, or once every 4,547 seconds.

The study corrected the damaging stereotype that men are far more sex-obsessed than women. While women recorded about half as many sex thoughts as men, they also thought less about other basic biological needs like eating and sleeping. Overall, gender was a poor predictor of how often a person thinks about sex; emotional attitude and comfort level with sex were both more indicative.

3. People only use 10% of their brains.

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Mayo Clinic neurologists, Princeton neuroscientists, and the distinguished staff of MythBusters have all debunked — and ridiculed — the idea that 90% of our brains are sitting inert inside our heads. The brain is a complex organ with different areas that serve different functions, and virtually every part sees activity over the course of a single day.

4. Gun ownership has been increasing.

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Though gun sales are going up, the portion of the population that owns guns is declining.

5. Being in the military makes people commit suicide.

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It's true that per capita there are more suicides in the military than in the general population. But the military is made up of a male-heavy demographic more susceptible to suicide. After controlling for a few factors like age, sex, and race, the military actually has a lower suicide rate than the country as a whole.

6. Alcohol is the most harmful drug.

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This Lancet study, released in 2010, sparked headlines about how "alcohol is shown to be more harmful than heroin or cocaine." But notice that most hard drugs were found to be more harmful to users than alcohol. The distinction of "most harmful drug" was given to alcohol because of its widespread use and effect on society as a whole, not because having a beer is more dangerous than shooting up.

7. Humans had shorter life spans in prehistoric times.

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In pre-modern times, human life expectancy was sometimes in the twenties or thirties. But this doesn't mean that people naturally started dropping dead at 29; high infant mortality rates brought down the average life expectancy of the population. Life span, which generally refers to the age that the oldest members of the population live to see, could be just as high.

8. Only 1 in 10 Americans has a passport.

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This figure is thrown around sometimes as evidence of the U.S.'s insularity. But it's false — the real number is around 37%.

9. Marijuana is a gateway drug.

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Suggesting that marijuana acts as a "gateway" to harder drugs confuses correlation with causation. Most abusers of hard drugs have used marijuana in the past, in part because someone willing to do hard drugs would no doubt also be willing to use a less harmful and more readily accessible drug like marijuana.

But the claim that marijuana use causes later hard drug use is a dubious one. In 1999, the Institute of Medicine at the National Academy of Sciences stated, "There is no conclusive evidence that the drug effects of marijuana are causally linked to the subsequent abuse of other illicit drugs." Later studies have shown that the association between marijuana and hard drugs does not necessarily suggest a causal link. In fact, places like Holland that have looser drug laws and increased access to marijuana actually have lower rates of hard drug use.

10. All data can be plotted on a bell curve.

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It's a common error to believe a bell curve (or normal distribution) applies to pretty much any set of data. Natural phenomena, like height, do often fall into a bell curve distribution, and that's why it's a tool frequently used in hard sciences like physics or chemistry. But using these same tools in more unpredictable realms, like economics or other social sciences, can get us into trouble: Models used to predict stock market behavior often give 1 in 1 billion odds to the type of crashes that now occur virtually once a decade.

Writer Nassim Taleb gives this example in his book The Black Swan: A thousand people are gathered in a room, and the world's tallest person walks in. The average height in the room wouldn't change much — maybe skew up by a decimal point or two. But if Bill Gates walks in, another unlikely, if plausible event, the average wealth in the room would change immensely — so much so that the combined wealth of the other 999 people would probably be an afterthought. A bell curve would describe the height distribution of people in the room pretty well — the wealth distribution, not so much.