The following is summarized from information provided by American Mensa.
The history of IQ testing — In the early 1900s Alfred Binet was commissioned by the French government to devise a test to enable school authorities to predict academic success. He developed a formula that calculated the abilities measured for a given student divided by the average abilities for that age group multiplied by 100 (hence, the term “Intelligence Quotient”).
Early IQ testing in the U.S. — In the 1920s, Lewis Terman, a professor at Stanford, applied these methods for California schools, developing the Stanford-Binet IQ test.
The IQ model changes — In 1939 David Wechsler pioneered new testing procedures using a statistical model of ability ranges and variance. This is the same model we use today.
Today’s meaning of “IQ” — Although we still use the term “IQ,” it is no longer a true quotient, but rather a statistic. An individual’s test score is correlated to a percentile based on the overall range and distribution of the test scores. The percentile indicates how much a score deviates from the average.
How standardized tests work — Standardized tests, including the tests Mensa offers, are “normed,” so a person’s score is compared against the scores of a large group of people who have already taken the same exam, called the “norming group.” The norming process provides a “bell curve” distribution of scores in the general population, with an average (mean) score of 100. Nearly 70 percent of the population has an IQ between 85 and 115 on most tests. The scores above 115 are generally considered as “high IQ,” and those above 130 to 132 (depending on the test) are in the top 2 percent of the population.
An IQ score is meaningless without the name of the test — Different tests are normed differently, so an IQ of 130 on one test could be the equivalent of an IQ of 140 on another test.
The answer to the Big Question: “If you’re so smart, why aren’t you rich?”— A high IQ is not necessarily an indicator of wealth, ambition or career success. It simply indicates that a person has higher-than-average reasoning abilities. Interestingly, testing reveals that highly creative people often do poorly on standardized tests because they use their test time thinking of broader applications to simple questions. For example, both Albert Einstein and Thomas Edison were failures in public schools and did poorly on exams.