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IQ: What Are the Odds You’re a Genius?

Stephen Hawking is charmingly evasive about his IQ. In 2004, he told the New York Times, “I hope I’m near the upper end of the range.” Chances are he is. His IQ is almost certainly high enough to qualify him for Mensa, the biggest high-IQ society on Earth—one in fifty people will meet its membership criteria. But would he qualify for the ultra-exclusive Pi Society, which takes only those with IQs in the top 99.999999 percentile?

Many geniuses haven’t. Had they been given the chance, the top minds behind the founding of Mensa, or even those behind the creation of IQ testing itself, might not have made the cut.

The idea of measuring brainpower began in the late 1800s with Sir Francis Galton, a privileged Victorian-era Englishman who had more than enough brains of his own to measure. He invented, among other things, fingerprint analysis, weather maps, the concept of mathematical correlation, the phrase “nature versus nurture,” and psychometry—the measuring of intellect.

The idea came to him after reading his half-cousin Charles Darwin’s The Origin of Species.

Determined to quantify the (to him) obvious differences between upper- and lower-class brains, he threw himself into the study of genetic superiority. He even gave it a name—“eugenics”—and psychometry grew out of it in the late 1800s.

The “science” of eugenics was eventually dismissed as racist baloney, but the notion of testing for intelligence persisted.

Psychologists and statisticians devised many ways to test smarts over the ensuing years. In the first years of the twentieth century, Frenchmen Alfred Binet and Théodore Simon created the first version of today’s stereotypical brainpower test: it measured one’s “mental age,” divided it by actual age, and multiplied the quotient by 100—giving an intelligence quotient, or IQ.

Their system had problems. For example, the only limit to IQ was one’s age: a twenty-year-old found to have the mental age of a forty-year-old (whatever that means) would have an IQ of 200. In theory, a ten-year-old found to have the mental age of an eighty-year-old could have an IQ of 800. Such a system only works in a world where older is always smarter.

To address this flaw, in 1939 American psychologist David Wechsler refined the method. He compared an individual’s performance to the general population’s, rather than to his or her own mental age. The deviation from average becomes the IQ.

This system is the basis for most IQ tests today. “Average” is 100. It splits the population right down the middle: the odds a person will have an IQ of 100 or higher are 1 in 2.

To qualify for membership in Mensa, your IQ needs to be in the top 2 percent—around 130 or higher. It’s the top 2 percent and not the top 1 percent due to, of all things, a math error. The founders of Mensa International created their society just after World War II on the principle that—after such terrible conflict—it would be an apolitical group, ideology-free, open only to the wisest of Britons, the top 1 percent. However, someone made a mistake calculating IQ standard deviations, and Mensa has accepted the top 2 percent ever since.

To have an IQ beyond the Mensa requirement is very rare. The odds a person will have an IQ of 140 or higher are 1 in 261.1, and the odds of having an IQ of, say, 160 or higher are 1 in 31,560—roughly the same as the odds that a person in Georgia over the age of four speaks Yiddish at home.

And it’s the rare folks who get invited in to the ultimate cerebral orders: the Mega Society and the Pi Society. The odds a person will meet the membership criteria for either group are set, as a rule, at 1 in 1,000,000. The required IQ is a whopping 172 or higher.

Just 6,700 people in the world, one in every million, could potentially pass the entrance exams. As you might imagine, these societies have scant membership. The Mega Society currently has twenty-nine members. The Pi Society has even fewer.

If the bar can go so high, what is the limit? What is the highest IQ ever recorded?

No one knows for sure. Most of the smartest people in history never took anything like an IQ test, and among those who may have, many are—like Stephen Hawking—not telling.

Marilyn vos Savant, formerly in Guinness World Records as having the highest IQ, received a 228 in the outdated Binet system; her result is no longer accepted. Similarly, an American named William Sidis, a prodigy at nearly anything—languages, mathematics, public transportation systems, the history of Native Americans—was once estimated to have had an IQ between 250 and 300, a range that’s essentially impossible in the current system. Psychometrists tend to agree that even under the best of conditions, the accuracy of very high IQs is iffy.

Critics of IQ testing also point out that there are many ways to be intelligent. Artists, chess champions, philosophers, Olympic medalists, authors, physicists, trivia masters, and linguists are all intelligent in different ways, many of which appear nowhere on an IQ test.

And according to Hawking, “People who boast about their IQ’s are losers.”

Originally published on Book of Odds