How is IQ traditionally calculated?

The traditional method for calculating IQ, or intelligence quotient, is based on the ratio of mental age to chronological age, multiplied by 100. This formula arose from the pioneering work of Alfred Binet and his colleague Théodore Simon, who created one of the first standardized intelligence tests. In this context, mental age refers to the level of intellectual functioning that a person demonstrates, as measured by their performance on various cognitive tasks, while chronological age is the actual age of the individual.

By using the formula of mental age divided by chronological age and then multiplying by 100, it allows for an understanding of intelligence relative to age. For example, if a child has a mental age of 10 and a chronological age of 8, their IQ would be calculated as (10/8) * 100 = 125, suggesting they are performing above the average level for their age group.

This method provides a clear numerical representation of a person's intellectual abilities compared to normative data for their age, allowing for a systematic approach to understanding intelligence. As such, this formula has been foundational in both psychological research and practical applications in educational settings.