French psychologist Alfred Binet first proposed the notion of IQ in 1905 while studying human intelligence in children with Theodore Simon. The two developed a test---referred to as the Binet-Simon scale---for determining the mental capacity of children, so that the less mentally apt ones could be given special attention. It wasn't until 1912, however, that the term IQ was coined by German psychologist William Stern in reference to Binet's scale. And in 1916 Lewis Terman, a psychologist at Stanford University in California, released new studies based on the original tests done by Binet and Simon. Today, most scores are based on this Stanford-Binet IQ scale.
The Stanford-Binet IQ scale scores intelligence as such: a person who scores less than 70 on an IQ test is thought to be distinctly lacking in mental capacity; a person who scores between 70 and 89 is classified as feebleminded or dull. Average intelligence is implied by a score between 90 and 109, while a person of superior intelligence scores between 110 and 140. Finally, a score above 140 is considered to denote genius or near genius. Ninety-five percent of the population is thought to have IQs between 60 and 140, but only 50 percent of the population scores between 90 and 110.
Often, IQ test scores will only reflect mental capacity in terms of mathematical, spatial or logical reasoning, in addition to determining an understanding of language. The score does not take into account wisdom, experience or virtue, all of which determine emotional intelligence and the ability to make sound choices. A person could excel at these other skills, but not have a very high IQ. Thus, many find fault with determining a person's worth based on an IQ score.
Several external factors can affect IQ scores besides mental deficiency. A score will generally be lowered if a person is suffering from malnutrition, fetal alcohol syndrome or maternal addiction. In addition, the score can be lowered if the person has not been sufficiently educated. So, in schools with poor funding the scores are often unfairly low.
There are a few generalities that persist in the formulation of IQ scores. Generally, brain size can positively affect the score. Specifically, those with enlarged frontal lobes are able to consistently perform better. In addition, while men's and women's scores are in general equal, men seem to more often score in the extremes; their scores are often the lowest and highest.
In an evaluation of the IQ test and score, the American Psychological Association concluded that the IQ test, while faulty in some respects, was generally a decent predictor of school performance. In addition, it concluded that the IQ test could also fairly predict job performance. However, the APA also recognized certain racial biases present in the tests, as well as the role of genetic history in influencing the score. In fact, a debate continues today about the role of nature and nurture in determining an IQ score.