Intelligence quotient, also called IQ, is a number used to indicate a person’s level of intelligence compared to other people. The average IQ is set at 100 for convenience. In reality, any number could be used as the average. If a person has an IQ twice as high as another person’s, however, it does not mean that the first person is twice as intelligent.
People with IQ’s below 70 may be labeled as intellectually disabled, but only if they also show deficits in everyday adaptive behavior—that is, the ability to adjust to events in their daily lives. People with IQ’s over 130 may be labeled as intellectually gifted, but usually the individuals must show other kinds of outstanding performances to receive this label.
Calculating IQ.
Intelligence quotients are determined from tests of intelligence. These tests measure learning, memory, judgment, reasoning, and problem-solving skills. For example, a test might ask an individual to define a word, or the test might ask an individual to solve a word problem, such as high is to low as black is to? Or it might ask what number would come next in the following series of numbers: 18, 15, 12, 9, ?
Psychologists originally calculated intelligence quotients in a way that actually produced a quotient. They started with a mental age, which is the average age of a child who performs at a certain level. Thus, if an average 12-year-old answers 20 items correctly on a test of intelligence, then 20 correct answers corresponds to a mental age of 12. Then psychologists took into account chronological age, the length of time a person has lived. If a child is 10 years old, that child’s chronological age is 10. The IQ score was calculated from the following formula: IQ = ([Mental age] ÷ [Chronological age]) x 100.
Thus, someone with a mental age of 10 and a chronological age of 10 has an IQ of 100. Someone with a mental age of 8 and a chronological age of 10 has an IQ of 80.
Today, testers rarely compute IQ’s in this way. Increases in people’s mental age do not occur evenly across age levels. The procedure for calculating IQ only works for people up to about age 16 to 18. People’s mental age increases at a slower rate as they grow older until it stops increasing altogether and may even decrease.
Some intelligence tests produce just a single IQ score, but most tests produce multiple scores. For example, one kind of test produces an overall IQ score, but also scores for verbal IQ and performance IQ. The verbal IQ is based on problems largely involving words. The performance IQ is based largely on tasks that require manipulation of puzzlelike materials.
Problems of intelligence testing.
Critics have pointed out several problems with intelligence testing. The tests may not be equally fair for all groups. For example, someone who grows up speaking a language other than English will clearly face a disadvantage on a test given in English. Educators and psychologists have attempted to create tests that reduce or even eliminate the effects of culture and language, but no such tests have been completely successful.
There is also a risk that a person’s score on an IQ test will give the impression that the person’s abilities cannot vary and lead to the person being labeled. But labels can be misleading because people’s IQ scores do fluctuate.
In addition, psychologists have many theories of intelligence, and not all of them agree that a single test can accurately measure it. Many believe that IQ scores represent only part of the full range of a person’s intellectual abilities.
