The science behind IQ tests
Have you ever wondered what your IQ is and more to the point what it actually means in terms of intelligence?
The term IQ (from the German Intelligenz-Quotient) was pioneered by German psychologist William Stern in 1912. It is a score derived from several standardised tests intended to assess intelligence.
The first intelligence test was known as the Stanford-Binet scale and was created by the French psychologist Alfred Binet. He was interested in studying mental retardation in school children and devised a series of tests to assess their intelligence.
These tests were both physical and mental, including the ability to draw abstract designs and identify various body parts, and with these tests, he was able to assess what he called “mental age”.
This is an individual’s level of mental development in relation to that of other children.
The variation of the Stanford-Binet test used today follows the formula:
IQ = (Mental age / Chronological age) x 100
This works particularly well in testing children. For example, if testing a 10 year old’s IQ, a series of tests will be compiled ranging from a 9 year old’s average ability to an 11 year old’s average ability. If the child answers all the questions for the 9 and 10 year olds, it can be assumed his mental age matches his chronological age. Thus his IQ would be:
IQ = (10/10) x 100 = 100
Average IQs range between 90 and 110 with a score of over 140 considered superior whilst a score under 70 is thought of as particularly low. However this test is more applicable to children; specifically to the gifted or mentally challenged individuals. The problem with applying it to adults is that there is controversy around the mental age issue – is there really a measurable difference between mental ages at 30 and 40?
A more appropriate test for adults is the Wechsler Adult Intelligence Scale (WAIS IV). It is considered a more rounded scale for calculating IQs as it incorporates both verbal and non-verbal abilities. Wechsler defines intelligence as “the global capacity of a person to act purposefully, to think rationally and to deal effectively with his or her environment”. As opposed to a ratio of mental age to chronological age, IQ is now calculated as a deviation from a standard score.
The IQ values are represented as a bell shaped curve with the standard score of 100 at the top of the bell with most people deviating from it by plus or minus 15. The current version of the test is composed of 10 core subtests and five supplemental subtests. The ten core subtests comprise the full scale IQ. These subtests are divided through four index scores:
* Verbal Comprehension Index (VCI)
* Perceptual reasoning index (PRI)
* Working memory index (WMI)
* Processing speed index (PSI)
The test has been standardised from a sample of 2,200 people in the USA aged from 16-90. It is thought that 68% of adults should fall between the average range of 85-115.
So what are IQs used for? Generally it is thought to assess the brain’s skills like logic, verbal reasoning, memory, perception and mental arithmetic. Many areas of social science and psychology use it in their study. For instance, in education it can be used in predictions of educational achievements or special needs.
By social scientists it can be used to predict job performance and income. Most commonly though it is used in academia as a research tool. Social scientists in different fields will try to use IQ to correlate with parameters they are studying. In this instance, IQ has been shown to be associated with morbidity, mortality, parental social status and to a certain extent parental IQ.
However there is much controversy around the possible hereditary status of IQs. Different studies have found the heritability of IQ to be between 0.4 and 0.8, which means “substantially” heritable, although some completely refute this claim.
This brings us to the more compelling issue: does IQ really mean anything? Its reliability seems to depend on the people using it. While it is deemed highly reliable by psychometricians and reliable enough for clinical purposes by psychologists, others believe IQs cannot objectively represent an individual’s intelligence.
There are many criticisms among which that the test is biased in certain circumstances (with autistic children for example) and that the method of analysis is outdated. Also to be considered is that the same individual can have very different IQs depending on which scale has been used to calculate it which makes its reliability difficult to assess.
So all in all, whether you have a below average, normal or genius IQ, you shouldn’t fixate on it when it comes to the next exams! After all, it’s only a number.