In 1905, French psychologists Alfred Binet and Theodore Simon developed the first IQ tests, the Binet-Simon Intelligence Scale tests. As of 2010, the most commonly administered IQ tests are a revised version of the Stanford-Binet test and the Wechsler Adult Intelligence Scale.
Most IQ tests have a mean score of 100 and a normal bell-curve distribution. 68 percent of test-takers score between 85 and 115, while 96 percent score between 70 and 130. A score of 130 or higher places a test-taker in the top 2 percent, while a score below 70 means a person is in the lowest 2 percent.
IQ tests that do not have a mean score of 100 usually assign percentile rankings to scores. These percentile rankings show the percentage of the population whose scores you outrank. For example, if you scored in the 60th percentile, your scores are higher than 60 percent of the population.
IQ tests have been criticized for not measuring several aspects of intelligence, such as creativity, social skills or musical talent. In addition, intelligence has never been defined.