The purpose of measurement of intelligence or IQ is to find out individual differences in the general mental ability of different persons for a number of purposes like academic classification, occupational suitability and counselling etc.
Intelligent test can be defined as a test to evaluate general level of cognitive functions and intellectual ability.
To obtain an IQ score, the examiner divides a person's mental age (obtained through different tests) by his/her chronological age and then multiplies it by 100 to obtain his/her IQ.
However, as we know, mental growth stops at one point or the other in our life as we start growing. Therefore, our IQ score may start declining with age. So, for all practical purposes, IQ means mental age divided by chronological age and multiplied by 100 within the people of same age group.
History of Measurement of Intelligence
Biologist Sir Galton made a beginning with intelligence measurement tests. He thought that the intelligence could he measured by tests of sensory discrimination. He believed, for example, that the ability to discriminate heat, cold and pain may distinguish an intelligent person from a mentally retarded person.
Mekeen Cattel used the term 'Mental Test' for the first time in 1890. He devised tests covering muscular strength, speed of movement, sensitivity to pain, and memory etc. to measure the intellectual level of a person.
Alfred Binet's Contribution
French government had engaged Afred Binet to devise a diagnostic test to identify children with mental retardation. Therefore, together with a physician named Simon, he created a Binet-Simon Scale in 1905. This test had 30 pass/ fail items. Each item required mental and physical capabilities to complete the task.
Binet-Simon test was revised in 1908 but there were so significant changes. In 1911, it was again revised but the test was also extended to adults as it was previously only for judging mental retardation amongst children.
Abilities covered by the 1911 edition of Binet Simon test were language, auditory processing, visual processing, learning memory and problem solving. In 1916, M. Terman of Stanford University began revisions of this test and it came to be known as Stamford-Binet Intelligence Scale.
World War I and Tests for Army Personnel:
In 1914, American Psychological Association laid by Robert Yerkes devised intelligence tests for classification and selection of army personnel. Two tests were devised: (1) Army Alpha and (2) Army Beta. Both were group tests, the first was language test and second non-language performance test.
Revisions of Stanford Binet Test:
In 1937, Terman again revised Stamford Binet test and it came to be known as the Revised Stanford Binet Intelligence Scale. This revision included two alternate forms, L form and M form, each with 129 items.
Third revision of the Stamford Binet Test happened in 1960 after Terman's death and it was improved upon by Merill. It was called the Stanford Binet Intelligence Scale Form L-M. It included a deviation IQ with normative mean of 100 and a standard deviation of 16. This version included 142 important items from the previous edition of this test.
In 1986, Stanford Binet test was revised for the fourth time without any significant or crucial changes. SB-5 or the fifth edition of the Stanford Binet test was released in 2003. This edition is presently in vogue. This test is used to measure intellectual ability in individuals between the ages of 2 to 89 years. It contains 10 of sub-scales. The three arrears covered by SB-5 are:
(1) General Cognitive functioning,
(2) Verbal and non-verbal intelligence, and
(3) 5 CHC factors i.e. Fluid reasoning, knowledge, quantitative reasoning, visual-spatial processing, and working memory.
