What is IQ? How do psychologists classify people on the basis of their IQ scores?
In 1905, Alfred Binet and Theodore Simon made the first successful attempt to measure intelligence. In 1908, the scale was revised and the concept of Mental Age (MA) which is a measure of a person’s intellectual development relative to people of her/his age group. Chronological Age (CA) is the biological age from birth. Retardation was defined by Binet and Simon as being two mental age years below the chronological age.
The concept of IQ was devised by a German psychologist, William Stern in 1912. IQ means Intelligence Quotient (IQ) which refers to mental age divided by chronological age, and multiplied by 100.
IQ = (MA/CA) × 100
When MA = CA then IQ = 100
When MA > CA then IQ > 100
When MA < CA then IQ <100
\According to psychologists, IQ scores are distributed in the population in such a way that the scores of most people tend to fall in the middle range of the distribution. Only a few people have either very high or very low scores. The mean IQ score in a population is 100. People with IQ scores in the range of 90–110 have normal intelligence. Those with IQ below 70 are suspected to have ‘intellectual disability’, while persons with IQ above 130 are considered to have exceptional talents.