During the last half century, advancements in intelligence testing and genetics have greatly improved our understanding of intellectual disability, (ID, formerly mental retardation). One advancement was the development of psychological measurement technologies. This made it possible to distinguish different levels of functioning in people with ID. Another major advancement was the advent of learning theory. Learning theory spawned behavioral therapies during the mid-20th century. These therapies have enormous value for people with ID. The net result of these advancements is the provision of supportive services that match the unique abilities and needs of people with ID. These supportive services make it possible for people with ID to reach their true potential.
Advancements in Intelligence Testing
Alfred Binet was an unlikely contributor to the history of intellectual disabilities (ID, formerly mental retardation). He did not have a degree in psychology, nor was he a medical doctor. Binet earned a degree in law in 1878. After finishing law school, he took a great interest in psychology. He educated himself on the subject of psychology. His fascination with hypnosis led to an interest in human development and intelligence.
Binet worked as a researcher at Sorbonne University, Paris. In 1894, Binet received the distinguished title of Director of the Sorbonne's Laboratory of Experimental Psychology. He only worked there three years before earning this honor. He supervised a student named Theodore Simon. Simon was working towards his doctorate. Together, Binet and Simon developed a test that measured children's abilities during different stages of development. The resulting test came to be known as the Binet-Simon scale. It was the first intelligence test of its type.
Lewis M. Terman standardized the Simon-Binet Scale. Standardized tests permit comparisons between an individual, and the average for a group of similar people. Terman received his Ph.D. in 1905 from Clark University. He was interested in the study of intelligence and explored individual variations of intellectual functioning. He used a multi-test approach to make a distinction between different types of intelligence.
Terman was employed by Stanford University. There, he worked with a team of graduate students. They were interested in studying variations of intellectual development. Together they gathered data to revise the Binet-Simon scale. The final revision was published in 1916. The phrase 'intelligence quotient' first appears in this revision. It measured the ratio between mental and chronological age. The intelligence quotient (or IQ) was based on Binet's concept of "mental level."
Terman's revision of the Binet-Simon scale was renamed the Stanford-Binet. This test was the most frequently used measurement of intelligence up until the 1940s. Then the Wechsler Intelligence Scales emerged as the forerunner. Many years later, the Stanford-Binet is still a commonly used test of intelligence in children.
Henry Herbert Goddard was another psychologist who worked with the Binet intelligence test. He translated the Binet scale into English in 1908. He then distributed the test throughout the United States. Goddard worked as the Director of Research at Vineland Training School for Feeble-Minded Girls and Boys in the state of New Jersey. This facility was the first facility dedicated to the study of intellectual disabilities. Goddard advanced the use of IQ tests to identify intellectual disability.
In 1910, Goddard introduced a classification system of severity. His classification was based on the intelligence quotient. Goddard used the term "moron" for the mildly impaired. The severely impaired were labeled "imbecile." The term "idiot" was reserved for profound intellectual disabilities. Unlike today, when these terms were first introduced, they were neutral in meaning.
Goddard was highly interested in eugenics. Practitioners of eugenics were concerned with improving the human gene pool. To achieve this goal they believed it advantageous to rid the population of people considered inferior, defective humans. The most devastating application of eugenics was Adolf Hitler's attempts to exterminate persons of Jewish decent. Goddard applied eugenic principles to people with ID. He was very concerned with preventing persons with ID from reproducing. He thought segregating people with ID would solve this reproductive 'problem.' He felt this was a viable alternative to compulsory sterilization. He apparently preferred compulsory sterilization. He thought sterilization was a more permanent solution. However, he recognized that sterilization was unlikely to gain acceptance in the United States.
The Binet tests were used extensively throughout the early part of the twentieth century. The Stanford-Binet is still in use today. However, another set of intelligence tests are more commonly used today. These are tests developed by psychologist David Wechsler. Among the Wechsler tests are: 1) the Wechsler Adult Intelligence Scale (WAIS); 2) Wechsler Intelligence Scale for Children (WISC); and 3) the Wechsler Preschool and Primary Scale of Intelligence (WPPSI). Wechsler is responsible for standardizing IQ scores across different tests. Each test has a mean (average) score of 100. Each test has a fixed standard deviation of 15. He also introduced the idea that intelligence has two main components. These are verbal and performance (or spatial) components. Each yields a separate domain-specific IQ score. You can learn more about these psychological tests here.