Fantasy world

"Mental Age"

Alfred Binet, 1857-1911

It's a matter of everyday experience that some people are smarter than others. But how do we measure "smartness"?

In 1905, a French psychologist by the name of Alfred Binet, working with a physician-associate, Theodore Simon, developed the Binet Simon Test designed to measure the intelligence of retarded children, based upon their observations that.

(1) Just as children grow taller as they grow older, they grow more mentally capable as they grow older; and

(2) Some children can perform at age and equivalent-grade levels above their chronological ages, while other children perform at age and equivalent-grade levels below their chronological ages. For example, a few 6-year-olds could perform as well on the Binet Simon mental tests as the average 8-year-old, while a few 6-year-olds could only perform as well as the average 4-year-old.

In 1911, the concept of "mental age" (as distinguished from "chronological age")
was introduced. The 6-year-old who performed as well as the average 8-year-old was assigned a mental age of 8, while the 6-year-old who performed only as well as a 4-year-old was assigned a mental age of 4.

What Is "IQ"?

It was also observed that the gaps between children's mental ages and their chronological ages widened as the children got older. The 6-year-old with the mental age of 8 had a mental age of 12 by the time he was 9 and a mental age of 16 by the time he was12. Similarly, the 6-year-old with a mental age of 4 had a mental age of 6 when he was 9 and a mental age of 8 when he was 12. In 1912, the German psychologist, William Stern, noticed that even though the gap between mental age and chronological age widens as a child matures, the ratio of mental age to chronological age remains constant (and, as we will see, remains essentially constant throughout life). This constant ratio of mental age divided by chronological age was given the name "Intelligence Quotient". Actually, the intelligence quotient is defined as 100 times the Mental Age (MA) divided by the Chronological Age (CA).

IQ = 100 MA/CA.

Mental Age for Adults

At approximately. the age of 16, mental age, like height, stops increasing. Until 1960, it was customary to use 16 as the divisor for mental age among adults. Actually, certain mental functions increase slowly and slightly after the age of 16, peaking in the 20's, with others remaining stable or even rising slightly up to the age of 60 or so. With some individuals, vocabulary may increase over time.

The Practical Significance of IQ

The average IQ of the population as a whole is, by definition, 100. IQs range from 0 to above 200, and among children, to above 250. However, about 50% of the population have IQs between 89 and 111, and about 80% of the population have IQs ranging between 80 and 120, with 10% lying below 80, and 10% falling above 120. For IQs below 120, IQ is the best predictor of socioeconomic status of any psychometric measurement. In more complex jobs, IQ is better than even education or experience at predicting job performance. In her article "The General Intelligence Factor", Scientific American Presents "Exploring Intelligence", pg. 24, 1999, Linda Gottfredson states,"Adults in the bottom 5% of the IQ distribution (below 75) are very difficult to train and are not competitive for any occupation on the basis of ability. Serious problems in training low-IQ military recruits during World War II led Congress to ban enlistment from the lowest 10% (below 80) of the population, and no civilian occupation in modern economies routinely recruits its workers from that below-80 range. Current military enlistment standards exclude any individual whose IQ is below about 85."

"Persons of average IQ (between 90 and 100) are not competitive for most professional and executive-level work but are easily trained for the bulk of jobs in the American economy. By contrast, individuals in the top 5 percent of the adult population can essentially train themselves, and few occupations are beyond their reach mentally."

"People with IQs between 75 and 90 are 88 times more likely to drop out of high school, seven times more likely to be jailed, and five times more likely as adults to live in poverty than people with IQs between 110 and 125. The 75-to-90 IQ woman is eight times more likely to become a chronic welfare recipient, and four times as likely to bear an illegitimate child than the 110-to-125-IQ woman."

In his book, "Straight Talk About Mental Tests", The Free Press, A Division of the Macmillan Publishing Co., Inc., New York, 1981, pg. 12, Dr. Arthur Jensen cites the following four IQ thresholds:

(1) An IQ of 50 or below. This is the threshold below which most adults cannot cope outside of an institution. They can typically be taught to read at a 3rd or 4th grade level. However, they cannot normally function in the customary classroom setting, and they require special training programs.

(2) An IQ between 50 and 75. At this level of intelligence, they generally cannot complete elementary school. Most adults will need smarter help in coping with the world.

(3) An IQ between 75 and 105. Children in this IQ range are not generally able to complete a college prep course in high school.

(4) An IQ between 105 and 115. May graduate from college but generally, not with grades that would qualify them for graduate school.

(5) An IQ above 115. No restrictions.

For IQs in these ranges, the influence of IQ upon socioeconomic status is dramatic. 31% of those with IQs below 75 were on welfare, compared with 8% of those in the 90 to 110 IQ interval, and 0% in those with IQs above 125. 55% of mothers with IQs below 75 went on welfare after the birth of the first child, compared with 12% of those with IQs between 90 and 110, and 1% of those with IQs above 125. Income is highly dependent upon IQ up to an IQ-level of about 125.