The first attempts to measure intelligence were made by Francis Galton and Alfred Binet. Their ideas were almost polar opposites. Galton believed intelligence was largely inherited whereas Alfred Binet emphasized the effect of the environment on intelligence. Binet and Théodore Simon developed one of the first intelligence tests, which was published in 1916. This test was made to detect children who were in need of special education. The early intelligence tests were not able to compare people who had different chronological ages, however. That's why William Stern suggested using an intelligence quotient (IQ):
Mental age (MA) divided by chronological age (CA), multiplied by 100.
Although modern IQ tests are quite different from the first tests, IQ scores are still derived from standardized intelligence tests.
Definition
How is intelligence defined? Many psychologists seem to agree that an intelligent person can learn from experience and adapt to his environment. As a result, he can make a mistake once, but won't repeat the mistake. He can also be moved from one environment to another, and he'll acclimate to his new surroundings. More modern theories of intelligence also emphasize that an intelligent person is able to understand and control his thinking process during problem solving and decision making. You can't forget that culture has a big role in what is considered intelligent. What's considered intelligent in one community may not be in another.
What Is Measured?
A typical IQ test consists of numerous problems that the subject must solve under supervision and within a limited time. These tasks are designed to measure general ability to solve problems, understand concepts, perceive relationships between things and store or retrieve information. Typical IQ tests measure memory, spatial, mathematical and language-related abilities. One of the most well-known IQ tests is the Wechsler Adult Intelligence Scale-IV Edition (WAIS-IV), which consists of seven verbal (information, comprehension, arithmetic, similarities, vocabulary, digit span and letter-number sequencing) and seven performance (digit symbol-coding, picture completion, block design, matrix reasoning, picture arrangement, symbol search and object assembly) sub-tests.
Correlation
Certainly, there's a strong correlation between a high IQ score and high intelligence, but the IQ score correlates with many other qualities as well. For example, it's been shown that people with higher IQs have generally lower adult sickness and death rates. Likewise, low IQ scores correlate strongly with poor health. A study published in the Journal of Neurology, Neurosurgery and Psychiatry in 2004 says that a decrease in IQ has been shown to predict Alzheimer's disease and dementia a decade later. The IQ score also correlates with school performance, according to the American Psychological Association's report "Intelligence: Knowns and Unknowns," published in 1995. Even stronger correlations have been found between high IQ score and self-discipline. Interestingly, high IQ scores correlate with your success at work and with your income only up to a point. A study published in the journal Intelligence in 1989 found that if your IQ is very high, it doesn't seem to bring you any more money or success at work than a reasonably high IQ does.
Score Distributions and the Flynn Effect
The scoring of modern IQ tests is based on a projection of the subject's measured rank on the Gaussian bell curve with the average IQ being 100 and a standard deviation of 15. People who score lower than 70 are typically considered developmentally disabled. Those scoring higher than 145 are considered to be geniuses. Intriguingly, average IQ scores have been rising about three points per decade since the early 20th century. It's difficult to explain this phenomenon, called the Flynn effect, but it's been speculated that it may be due to improved nutrition, or better education, although some scientists have also suggested that the improved IQ scores don't reflect real changes in intellectual abilities, but are mainly due to methodological problems in the IQ tests.
Criticisms of IQ Tests
One common critique most IQ tests face is that they leave out many areas that might be considered part of intelligence. These include, for example, creative abilities and musical affinity. How about measuring your abilities to get along with people? Standard intelligence tests are rarely appropriate for certain patient groups such as children with autism and dyslexia. Also, it's been said that IQ tests were built for white subjects and that many of them are culturally biased.
References
- "Inquiry into human faculty and its development"; Galton; 1883
- "Psychological Methods of Intelligence Testing"; Stern; 1912
- "The development of intelligence in children"; Binet, Simon; 1916.
- Intelligence (journal); "Correlations of mental tests"; Detterman, Daniel; vol. 13, 349-359, 1989.
- Journal of Neurology, Neurosurgery and Psychiatry Journal; "Premorbid cognitive testing predicts the onset of dementia and Alzheimer's disease better than and independently of APOE genotype"; Cervilla, Prince, Joels; vol. 75, 2004.
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