How is IQ Measured or Calculated?

How is IQ measured across different tests? From vocabulary to pattern recognition, learn why different tasks still measure the same intelligence ability.

Dr. Russell T. WarneChief Scientist

IQ is measured with intelligence tests, which are psychological tests designed to elicit behaviors that show the examinee’s intelligence. Often called “IQ tests,” these tests consist of tasks that require people to think abstractly, solve problems, demonstrate past learning, or reason.

An IQ test may ask examinees to define words, identify patterns, reason about different ideas, or recall ideas from their short-term memory. There is no one task that appears on every IQ test. Some of these tasks may appear trivial. For example, many tests use a task called “digit span,” which is a measure of short-term memory in which the examinee must repeat back a series of 1-digit numbers that have been read to them. This simple task is a good measure of short-term memory, and it appears on IQ tests because smarter people can remember longer sequences than less intelligent people.

The deceptively simple nature of some tasks on IQ tests have led some people to conclude that IQ doesn’t really measure anything important. Those people are dead wrong. What matters is not the appearance of the task; instead, what matters is what the task requires people to do. Any task that requires people to think, reason, or engage in any cognitive effort will measure intelligence to some extent. Over 100 years ago, British psychologist Charles Spearman identified this principle and called it the “indifference of the indicator.”

The indifference of the indicator does not mean that every task measures intelligence equally well, however. Some tasks are better than others, and those appear most frequently on intelligence tests. Vocabulary and matrix reasoning tasks, for example, often appear on IQ tests because they seem to be better measures of intelligence than many other tasks. But there are some IQ test creators that have chosen other tasks instead. It is not necessary for different IQ tests to use the same tasks to measure intelligence. Regardless of the collection of tasks, different IQ tests still measure the same general intelligence ability.

IQ tests not only vary in their tasks, but they also vary in their mode of administration. The oldest administration method is by a psychologist or other qualified clinician in a one-on-one setting. Other tests are administered in person in group settings, either on a computer or with a pencil and paper. Online, self-proctored IQ tests are also an option in the 21st century. Again, the mode of administration does not matter; all of these tests measure intelligence. There may be reasons (such as cost or logistics) that a test user may prefer one administration method over another.

Watch “What Actually Makes an IQ Test Biased? (Not What You Think)” with Craig Frisby on the Riot IQ YouTube channel to see how scoring methods and test design influence IQ measurement.