IQ scores are also used by social scientists; in particular, they study the distribution of IQ scores in populations and the relationships between IQ score and other variables. IQ correlates with job performance and income, also with the social status of the parents.

IQ Hereditary Factors

Recent work has demonstrated links between IQ and both morbidity and mortality. It is as yet unproven as to whether IQ is inherited.

IQ Environmental Factors

Environmental factors play a role in determining IQ. Proper childhood nutrition appears critical for cognitive development; malnutrition can lower IQ. Other research indicates environmental factors such as prenatal exposure to toxins, duration of breastfeeding, and micronutrient deficiency can affect IQ.

IQ Learned Factors

It is possible to increase one's IQ score by training, for example by regularly playing puzzle games, or strategy games like Chess. Early musical training is also thought to increase IQ.

IQ Age Factors

IQ of the same person may vary with age, and the average IQ scores for many populations are rising at an average rate of three points per decade, with most of the increase in the lower half of the IQ range: a phenomenon called the Flynn effect.

It is disputed whether these changes in scores reflect real changes in intellectual abilities, or merely methodological problems with past testing..

IQ Tests

Most IQ tests are composed of several different subtests. These tests yield both an overall score and individual subtest scores.

A typical IQ test requires the test subject to solve a number of problems in a set time under supervision. IQ test items include various domains, such as:

short-term memory
verbal knowledge
spatial visualization
perceptual speed.

Some tests have a total time limit, others have a time limit for each group of problems, and a few are untimed, unsupervised tests, typically geared to measuring high intelligence.

IQ tests are calibrated in such a way as to yield a normal distribution, or bell curve. The center value (average IQ) is 100, with a standard deviation of 15 or occasionally 16.

Each IQ test, however, is designed and valid only for a certain IQ range. Because so few people score in the extreme ranges, IQ tests usually cannot accurately measure very low and very high IQs.

Different individuals exhibit different IQ scores, depending on the individual these may or not be stable over their lifetime.

High IQ Societies

There are several organizations or societies where membership is limited to those above a certain iQ. The most well known is MENSA International, which requires members to score in the top 2% of a standardized IQ test.

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