Most people think of intelligence as describing "how smart" someone is. However, the actual definition is quite a bit more complicated than that. Psychological researchers and theorists have actively debated and argued over how to best define and measure intelligence for over one hundred years. Individual theorists and researchers have disagreed on which mixture of cognitive skills and mental capacities (problem solving, abstract thinking, creativity, memory, concentration, interpersonal skills, body/movement skills, etc.) should be included within the definition, and how to measure these important attributes in a fair, culture free manner. At present, intelligence is best thought of not as a single ability or attribute, but rather as a global construct encompassing many different and separate cognitive abilities. According to the American Psychological Association, intelligence describes a person's ability to understand complex ideas, to adapt to the environment, to learn from experience, and to engage in reasoning and decision-making in all sorts of situations (both new and familiar).
History of Intelligence Testing and IQ Score
One way to understand the complexity involved in defining intelligence is to look at how tests measuring this construct have evolved over time. The first scientific test of intelligence, constructed by Alfred Binet during the early 1900's, was designed to provide French educators with a reliable method for discriminating special needs children from the general school population for purposes of classroom placement. Binet used children's test scores across a series of tests to separate children who needed special education classes from youth who could function well in regular classes. Binet's approach attempted to measure children's "general mental ability" by assessing different facets of their reasoning and thinking abilities and then using these scores to predict the learning environment likely best suited to each child.
In 1905, Binet and colleague Theodore Simon updated Binet's previous test to create the Binet-Simon scale, again for the purpose of identifying students in need of special education. The primary advance with this second intelligence test was that the Binet-Simon score was computed so as to take into account each student's chronological age. Since children's raw abilities and capacities typically advance and expand as children develop over time, it had become apparent that it was impossible to talk about intelligence without taking age into account. Without taking age into account, a truly smart child would appear (but not actually be) less intelligent than a less cognitively gifted adult simply because the adult is more cognitively mature and experienced than the child. Consequently, in computing the intelligence of children, it is vital that ability comparisons be made in comparison to similarly aged people, and not to all people of all ages.
Stanford University psychologist Lewis Terman released the "Stanford Revision of the Binet-Simon Scale," (now known as the Stanford-Binet and still in use today) in 1916. This test defined intelligence in terms of four separate cognitive factors:
- verbal reasoning (e.g., the ability to solve verbal problems and to demonstrate language mastery through demonstrations of vocabulary knowledge and sentence comprehension)
- quantitative reasoning (e.g., the ability to solve math problems)
- abstract/visual reasoning (e.g., the ability to solve problems requiring comprehension of complex relationships between geometric shapes)
- short-term memory (i.e., the ability to hold facts in memory for a short period of time).
Terman's test also resulted in a comprehensive score that he called an "intelligence quotient"; what we call today an "IQ". In the manner of the Binet-Simon scale, each student's IQ score was computed based on a mathematical comparison of his or her tested mental age with performance expectations based on chronological age.
Today, the most commonly administered IQ test for children in the middle childhood stage of development is the Wechsler Intelligence Scale for Children, forth edition (WISC-IV) test, originally developed by David Wechsler in 1974, and last revised in 2003. The WISC-IV measures general intelligence (providing an overall IQ score) and also two broad cognitive factor scores: a verbal IQ score (measured with sub-tests that require listening and answering examiner questions, and measuring comprehension, vocabulary, and general information items), and a performance IQ (measured by timed problems that require children to physically manipulate puzzles, pictures, blocks, etc., rather than providing verbal answers to questions).
Though intelligence is measured with an eye to multiple competencies and takes a broad rather than narrow view of these abilities, there do appear to be several specific underlying cognitive abilities that strongly influence individuals' global intelligence. Children's speed of cognitive processing (i.e. their reaction time, or how quickly they can solve mental tasks) and their ability to use cognitive strategies effectively (i.e., how quickly they can select and use effective problem-solving strategies) strongly influence their measured global intelligence, with quicker, more efficient problem-solving children tending to have higher IQ scores. Cognitive speed and efficiency are considered aspects of children's information processing abilities.
There are a few take-home messages we hope to convey here. One is that intelligence is defined not as a measurement of a single monumental ability, but rather as multidimensional construct taking into account measures of a broad array of abilities and talents. Another is that many of the sub-tests comprising modern IQ tests are heavily culture-bound and draw upon children's past experiences and knowledge they have previously learned. It is quite difficult, if not impossible, to measure intelligence in a pure raw form, separate from those things that intelligence enables people to accomplish, such as learning vocabulary or manipulating puzzles comprised of familiar shapes.