Intelligence tests (IQ tests) are designed to give an intelligence quotient derived from a set of standardized test scores.Intelligence tests come in many forms, and some tests use a single type of item or question. IQ also correlates with job performance, socioeconomic advancement, and "social pathologies". Recent work has demonstrated links between IQ and health, longevity, and functional literacyModern IQ tests produce scores for different areas (e.g., language fluency, three-dimensional thinking, etc.), with the summary score calculated from subtest scores. The average score, according to the bell curve, is 100. Individual subtest scores tend to correlate with one another, even when seemingly disparate in content.
Various IQ tests measure a standard deviation with different number of points. Thus, when an IQ score is stated, the standard deviation used should also be stated. A result of 124 in a test with a 24-point standard deviation corresponds to a score of 115 in a test with a 15-point deviation.Where an individual has scores that do not correlate with each other, there is a good reason to look for a learning disability or other cause for the lack of correlation. Tests have been chosen for inclusion because they display the ability to use this method to predict later difficulties in learning.The role of genes and environment (nature and nurture) in determining IQ has been debated for decades and the degree to which nature versus nurture influences the development of human traits (especially intelligence) is one of the most intractable scholarly controversies of modern times.As it relates to intelligence, overall, except in unusual cases, the role of genes and heredity is far greater than the role of environment. However, environmental factors can, and do, play a role in determining IQ in extreme situations. 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 micronutrientdeficiency can affect IQ. In the developed world, there are some family effects on the IQ of children, accounting for up to a quarter of the variance. However, by adulthood, this correlation disappears, so that the IQ of adults living in the prevailing conditions of the developed world may be more heritable. It is reasonable to expect that genetic influences on traits like IQ should become less important as one gains experiences with age. Surprisingly, the opposite occurs. Heritability measures in infancy are as low as 20%, around 40% in middle childhood, and as high as 80% in adulthood.The heritability of IQ measures the extent to which the IQ of children appears to be influenced by the IQ of parents. Because the heritability of IQ is less than 100%, the IQ of children tends to "regress" towards the mean IQ of the population.