Who invented the IQ test and how is it used?

One of the first IQ tests was the Stanford-Binet test, introduced in 1905 by French psychologist Alfred Binet and his colleague, Theodore Simon. The Stanford-Binet test was created to identify children who might benefit from extra teaching in schools. Binet and Simon assumed that a lower IQ indicated a need for more teaching, not an inability to learn, an interpretation still held by some experts. The test gauged a child's ability to perform a series of tasks considered representative of their age group's abilities, and in this way gave an intelligence quotient or "IQ". Although modern IQ tests do not calculate scores in the same way, the terminology of those first IQ measures remains in common use.

Currently, the most common IQ test is the WISC-III, created in 1974 by David Wechsler and comprising a variety of problems typed by difficulty and skill requirements. The Bailey Scale of Infant Development is also widely used for testing infant cognitive development.

IQ Testing vs. "g"

In psychology, "g" is the abbreviation used for "general intelligence factor". In the case of IQ tests, an overall score is calculated by summarizing scores produced from different types of tests (such as 3-D thinking and language fluency). If an individual's scores across a variety of tests is examined, one sees a correlation, despite the disparate test-content. The term "g" describes what seems to be an underlying single factor in an individual's intelligence. There is an approximately 90% correlation between "g" and IQ.

Genetics and Environmental Influences on IQ

The most common method of determining the contribution of genetics to IQ is examining results of twin and adoption studies. The measure used is heritability, and scores go from 0 to 1 and are also expressed as percentages of variation due to gene variation. Studies so far have given an estimated score of heritability of 0.5, which means it appears that in the children studied half of the variation in IQ is because of gene variation.

The environmental effects of family on IQ appear only among children: in studies of adopted siblings with a shared family environment, the IQ correlation is .32 until adolescence. After adolescence, shared family effects on IQ disappear. Research into the effects of environmental factors such as nutrition or exposure to toxins seems to show a much larger influence in determining IQ than family environment.

Online IQ Testing

The growth of the Internet has seen IQ tests become easily accessible and extremely popular, with many websites offering the tests and, often for a fee, reports detailing your results. Buyer beware, however - the majority of Internet IQ tests are not validated by research and thus their worth as a measure of intelligence is unknown. Moreover, teh tests themselves may be skewed to the purveyor's purposes: for example, a company may give an IQ test to a prospective employee to determine their suitability for a particular job, and to this end they will weight the test to examine only those characteristics and skills that apply to a given position or job requirement.