An IQ of 100 is an average score. A score of 138 is in the 99.4 percentile, which means only 0.6 percent of the population has a higher IQ. Ninety-five percent of the population scores between 70 and 130.
There are a number of different tests that are used to measure IQ. The most widely used test is the Weschler Intelligence Scale. The Weschler testing method uses two separate scales for children and adults. IQs have been shown to have a direct correlation with mortality and social status. Additionally, IQs and education levels are also highly correlated.
Psychologist William Stern coined the term "IQ" in his 1912 book "The Psychological Methods of Testing Intelligence."