brain history

Intelligence testing developed out of a jealous man's attempt to upstage his cousin's rising popularity. Read on to find some interesting answers to your burning questions about the Intelligence Quotient.

Notable Geniuses

What is Intelligence?

  • Webster’s defines it as 1) The ability to learn or understand or to deal with new or trying situations; the skilled use of reason (2) the ability to apply knowledge to manipulate one's environment or to think abstractly as measured by objective criteria.


What is IQ, or Intelligence Quotient?

  • The technical definition is the ratio of tested mental age to chronological age, usually expressed as a quotient multiplied by 100. Conventionally, it’s expressed as a test score.


How did Intelligence Testing develop?

  • In the late 19th century, British scientist Sir Frances Galton wanted to prove that intelligence was a product of heredity and that it was also measurable. In his book Hereditary Genius, he compared the accomplishments and accolades of different generations from wealthy and prominent English families, then testing things that could be measured like eyesight, reaction time and skin sensitivity. Galton concluded that intelligence was in fact a product of genetics and could be preserved by good breeding.

  • Ironically, Galton’s intelligence theory was motivated by jealousy over his cousin Charles Darwin and his evolution theory. Darwin received plenty of attention for his strides in biology, and Galton wanted to upstage his cousin, thus developing his own theory.


What about the concept of Mental Age?

  • This concept assumes that all children follow the same path of intellectual development, but intellectually develop at different rates.


How did the concept of Mental Age develop?

  • French psychologist Alfred Binet developed the first intelligence test that successfully predicted academic success by using the concept of mental age. As mass education flooded French schools, the French Ministry of Public Instruction asked Binet in 1904 to develop a method of objectively identifying which students could not conform to formal education. The Ministry hoped that by identifying problem students and placing them in remedial classes, parents would pay more money for better schooling.

  • Unlike Galton, Binet found that testing practical knowledge, reasoning, vocabulary and problem solving were better indicators of mental ability and academic success than sensory reactions. Binet and his partner Theodore Simon developed an average standard for each age then compared this standard (the child’s mental age) to the child’s actual age. For example, if a 5 year old could successfully pass the standards for a 10 year old, then the child has mental age of 10.

  • Binet and Simon asked teachers to rate their students from best to worst and then tested each student themselves. Binet found that students rated higher by their teachers also rated higher on his test, thus creating an accurate predictor of academic success.


What about the first IQ test?

  • Stanford psychologist Lewis Terman revolutionized intelligence testing. Binet’s test never gained wide acceptance in France so a New Jersey school teacher brought the test to the United States to use on children with learning disabilities. Terman revised Binet’s test by adding questions for adults and establishing a new average standard of intelligence for each age. The first version was published in 1916 and called the Stanford-Binet Intelligence Scale.


Why was the Stanford-Binet test so much better?

  • Because instead of converting a person’s performance into a mental age, the Stanford-Binet test converted it into a single score, the intelligence quotient, which provided an easier basis for comparison.


How did the first Stanford-Binet test calculate IQ scores?

  • By dividing a person’s mental age by their actual age and multiplying it by 100. For example a 5 year old with a mental age of 10 would have an IQ of 200 (10/5 x 100).

  • While this scale was thought to be accurate for children, it was not an accurate predictor for adults. Since IQ is thought to level off in adulthood, the scale was revised and the current Stanford-Binet test no longer computes scores with this formula.


How does the Stanford-Binet compute scores now?

  • The 2003 edition provides multiple IQ scores, rather than just one number. There is a composite score measuring verbal and nonverbal areas of a child's development, a quantitative score measuring mathematical reasoning, and a memory score measuring short- term memory.


What are the most popular IQ tests now?

  • The Stanford-Binet, the Wechsler Intelligence Scale for Children and the Wechsler Intelligence Scale for Adults.


What are the differences between the Stanford-Binet and Wechsler tests?

  • The main difference is the Stanford-Binet test only tests children, while the Wechsler has an adult and child version. The Wechsler Intelligence Scale for Children, WISC, is divided into two main sections, the verbal and performance sections. The two main sections are divided into six and five subtests, respectively.


What are the WISC subtests?

  • The verbal section is divided into 1)information, which measures a child's range of factual information, 2)similarities, which measures a child's ability to categorize, 3)arithmetic, which measures the ability to solve computational math problems, 4)vocabulary, which measures the ability to define words, 5)comprehension, which measures the ability to answer common sense questions and 6)digit span, which measures short-term auditory memory.

  • The performance test is divided into 1)picture completion that requires telling what's missing in various pictures, 2)coding or copying marks from a code; 3)picture arrangement or arranging pictures to tell a story, 4)block design that requires arranging multi-colored blocks to match a design and 5)object assembly or putting puzzles together.


Did the U.S. Army ever use IQ tests to screen recruits?

  • Yes, American psychologist Robert Yerkes designed two tests to screen recruits during WWI, the Alpha Army and Alpha Beta tests. The Alpha test was for literate recruits and the Beta test was for the illiterate and non-English speaking recruits.

  • Unlike previous intelligence tests, the Army tests were administered to large groups of recruits all at once. Each recruit was assigned a letter grade A-D based on the amount of correct answers.

  • The highest-scoring recruits were elected to officer positions and the lowest-scoring recruits were not allowed to serve in the military.

  • The military still uses these IQ tests along with a long list of other tests to screen recruits. IQ tests are especially important to the military when determining who is eligible for a highly skilled jobs, such as jet pilot.



Email me -