Intelligence can be measured by tests. At the beginning of this century in Paris, Alfred Binet developed the first set of such tests to find out which children in school needed special attention. So, at the beginning, intelligence tests were mainly used to separate the dull children in school from the average or bright children so that they could receive special education; they were not meant to be free of cultural bias or academic content .
Intelligence is expressed in terms of IQ. Tests are developed, that indicate what an average child of a certain age can do; for example, what a 5-year-old can answer but a 4-year-old cannot. In other words, intelligence tests give us a norm for each age. A test is first given to hundreds of children in order to select those questions which the majority of children at that age can answer.
From such norms we may find that a set of questions for 5-year-olds is successfully answered by about 83 percent of children. These 83 in 100 children have average or above average intelligence. Of the remaining 17 percent of children, only about 3 percent do extremely poorly in the tests and are called mentally retarded children. The remaining 14 percent are sometimes called dull normal children. There is a graph which helps us understand the distribution of intelligence in a normal population.
Some of the questions in an intelligence test are verbal and they require oral or written responses. For example, a question in the verbal form is, “Apples are to oranges as tables are to … ?” The answer is any item in the furniture category, such as a chair, because apples and oranges belong to the category of fruit. Similarly, “Tall is to short, as up is to … ?” Another example would be to give the missing number in the series 4, 9, 19, 39….
A variety of questions are used in all standardized intelligence tests. All of them give age norms. If a 5-year-old child passes the tests that average children of the same age can pass, then his mental age is 5. On the other hand, if a 5-year-old child can only pass the test for age 3, then his mental age is 3. The IQ is calculated by dividing the mental age (MA) by the chronological age (CA) and multiplying the answer by 100. Thus in the first case the child has an IQ of 100 [(5 / 5) x 100] and in the second case an IQ of 60 [(3 5) x 100].
Therefore, IQ by definition is a measure of how well a child has done in the intelligence test compared to children of similar age. Nearly 67 percent of individuals have an IQ between 85 and 115. Those with IQs of 70 or below are considered to be mentally retarded and constitute some 3 percent of the population. Sometimes, we can understand the level at which a retarded or nonretarded child is functioning by referring to his or her mental age. Suppose we wish to place a retarded boy in a class with normal children, at what academic level should we place him? If his mental age is 7, he would be expected to do most of the class work for 7-year-olds in the school and he could be placed in class 3 or 4. He may, however, have a chronological age of 10.
As you probably know, physical and mental maturation cease in most children at the age of around sixteen. After this age an individual may gain knowledge and experience but, as far as his mental ability is concerned, he can learn whatever a 20-year-old can learn, given the same amount of training. Therefore, the highest mental age that a person can obtain in an intelligence test is 16. (There are, of course, intelligence tests designed for college students and adults who are superior in intelligence.
Therefore, if you wish to choose a group of highly intelligent students for an introductory course in a new field, such as how to track satellites, you may give the candidates an intelligence test for superior adults, along with a test of appropriate background knowledge.)