Intelligence is generally measured by the intelligence quotient (IQ) which indicates in its commonest form the position of S in relation to the population as a whole on a normally divided scale (mean value 1001; dispersion 15).
Normally, the designation “intelligence test” implies that the method concerned is assumed to measure “general intelligence” and not partial aspects of the latter. Psychologists are not, however, of one mind as to the performance areas covered by “g” or its structure; accordingly, the different intelligence tests are sometimes based on highly divergent models of intelligence. The earliest attempts at a psychological diagnosis of intelligence were made in the nineteenth century. Galton was the first to organize relatively large-scale systematic experiments to detect inter-individual differences in the sphere of intelligence. He postulated the standard distribution of intelligence generally accepted today.
Pioneering work was done by Binet who along with Simon in 1905 published the first procedures to justify the use of the term “intelligence test” in its present sense. Binet provided the original major impetus to the study of individual differences by means of standardized tests. While Binet’s method was designed for educational purposes as an intelligence test for children, the first intelligence test for adults were developed by military psychologists in America during the World War I.
They were the Army Alpha (verbal tests) and Army Beta (non-verbal) tests. These methods were suitable for use as group tests and were designed as test batteries (test batteries are a group of tests combined to make a single test) they therefore already possessed two major characteristics typical to most modern intelligence tests. The diagnostic possibilities of test batteries were subsequently extended by adding the psychological profile (test profile) formulated by the Russian psychiatrist G. J. Rossolimo. The psychological profile evaluated the interrelationship between the individual subtests on a differential diagnostic basis. The intelligence diagnosis method owes most of the qualitative improvements it has undergone to the use of statistical methods.
These methods enabled the tests to be designed scientifically and standardizes as measuring instruments. With the help of statistical methods, i.e.
factor analysis, it proved possible to obtain direct empirical access to the problem of intelligence, and to base intelligence tests on experimental findings.