How is IQ measured? Discover how IQ is tested through subtests, the g-factor, and how IQ scores are calculated for accurate assessment.
Dr. Russell T. WarneChief Scientist
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Can an IQ test capture the full scope of your cognitive abilities? These tests measure your ability to reason, solve problems, think abstractly, and learn quickly, which are core skills for tackling new challenges. Those are important aspects of intelligence, but they are not the full breadth of the human mind.
What Subtests Appear on IQ Tests?
There is no single type of question that appears on every intelligence test. Instead, IQ tests sample broadly across different cognitive abilities:
• Vocabulary questions that ask examinees to define words or identify synonyms
• Matrix reasoning tasks, in which test takers complete visual patterns
• Working memory tasks that require holding and manipulating information in the mind
• Processing speed tests that measure how quickly a person can perform simple cognitive tasks
• Spatial reasoning questions about how objects relate to each other in space
• Reaction time that gauges mental speed
To learn more about what these tests look like in action, watch this video:
Charles Spearman, one of the pioneers of intelligence research, argued that it doesn't matter what tasks appear on an IQ test, as long as they require thinking, judgment, or reasoning. He called this principle "the indifference of the indicator," and research has confirmed he was correct. This allows test creators to design assessments suited for different situations while still measuring the same underlying ability.
What is Missing from IQ Tests?
It is impossible to include every important aspect of the human mind on one test. Humans are incredibly complex. IQ tests measure a sample of what the brain can do as it reasons and solves problems. But humans are more than thinking machines. Personality traits, mental health, emotions, perceptions, interests, and other products of the mind are important, too. Some of these things have their own tests that are designed to measure them. The fact that IQ tests do not include these things is not a flaw of the IQ tests. Test creators have to limit the content of their tests because a test that measures everything that makes a person unique would be impossible.
Comparing Your IQ to Your Peers
Your IQ score tells you how your performance compares to other people in your age group, not the absolute amount of cognitive ability you possess. A 16-year-old and an 8-year-old can both have IQs of 100, even though the teenager has much more impressive cognitive abilities. Both are performing at the average level for their age, so both receive a score of 100.
Most IQ tests use a scale where 100 is average and each 15-point interval represents one standard deviation (which is a measure of how spread out each score is). About two-thirds of people score between 85 and 115, and about 95% score between 70 and 130.
What is the g Factor?
When psychologists analyze performance across different cognitive tasks, they consistently find something remarkable: people who do well on one type of mental task tend to do well on others. Someone who excels at vocabulary tends to also perform well on spatial reasoning. Someone who struggles with arithmetic often struggles with pattern recognition, too.
In 1904, Charles Spearman used a statistical technique he invented called factor analysis to identify what he called a "general factor" underlying these correlations. He abbreviated it as g, and many psychologists today consider g to be equivalent to general intelligence. Your IQ score is primarily a measure of this general mental ability, which explains why IQ scores predict performance across many domains, from school to the workplace to everyday problem-solving.
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