What Is an IQ Test?
An IQ test is an assessment that measures a range of cognitive abilities and provides a score that is intended to serve as a measure of an individual’s intellectual abilities and potential. IQ tests are among the most commonly administered psychological tests.
In order to understand what these scores really mean, it is essential to look at exactly how these test scores are calculated. Today, many tests are standardized and scores are derived by comparing individual performance against the norms for the individual’s age group. While many tests utilize similar methods to derive their scores, it is also important to note that each test is different and scoring methods may not be the same from one test to another.1
Types of IQ Tests
There are a number of different intelligence tests in existence and their content can vary considerably.2 Some are used with adults, but many are specifically designed to be administered to children.
Some commonly used intelligence tests include:
- Cognitive Assessment System
- Kaufman Assessment Battery for Children
- Stanford-Binet Intelligence Scale
- Universal Nonverbal Intelligence Test
- Wechsler Adult Intelligence Scale
- Wechsler Intelligence Scale for Children
- Woodcock-Johnson Tests of Cognitive Abilities
IQ tests can be used for a wide range of purposes including:
- Educational assessment and placement
- Assessment and diagnosis of intellectual disability
- Cognitive research
- Job candidate evaluation
- Assessing cognitive abilities including memory, speed, and attention
Modern intelligence tests often focus on abilities such as mathematical skills, memory, spatial perception, and language abilities. The capacity to see relationships, solve problems, and remember information are important components of intelligence, so these are often the skills on which IQ tests focus.
Impact of IQ Scores
Your IQ can have an impact on different areas of your life including school and work. High scores are often associated with higher achievement in school, while lower scores may be linked to some form of intellectual disability.3
The following is a rough breakdown of various IQ score ranges. Some tests present scores differently and with differing interpretations of what those scores might mean.
|120 to 129
|110 to 119
|90 to 109
|80 to 89
|70 to 79
|69 & below
These classifications come from the Wechsler series of IQ tests for children and adults.
Intelligence test scores typically follow what is known as a normal distribution, a bell-shaped curve in which the majority of scores lie near or around the average score. For example, the majority of scores (about 68%) on the Wechsler series of intelligence tests tend to lie between plus 15 or minus 15 points from the average score of 100.
This means that approximately 68% of people who take this test will score somewhere between 85 and 115. As you look further toward the extreme ends of the distribution, scores tend to become less common.
How common are very high IQ scores?
Very few individuals (approximately 0.2%) receive a score of more than 145 (indicating a very high IQ) or less than 55 (indicating a very low IQ) on the test.
In many cases, an IQ score that falls below 70 is considered low IQ, while a score of about 140 indicates high IQ. In the past, scores below 70 were used as a marker to identify intellectual disabilities. Today, test scores alone are not enough to diagnose an intellectual disability and diagnosticians also consider factors such as the age of onset and adaptive skills.
Tips for Making Sense of Your Score
In order to understand what your score really means, it can be helpful to understand how IQ tests are designed and how your scores compare to others. Your score on an IQ test can tell you more about how you compare to others in your peer group with regards to things such as:
- Language skills
- Mathematical abilities
- Processing speed
- Reasoning abilities
- Visual-spatial processing
In order to adequately assess and interpret test scores, scientists who develop IQ tests use a process known as standardization. This involves administering the test to a representative sample of the entire population that will eventually take the test.1
This initial sample represents the total population as accurately as possible and reflects many of the things that are present in the general population. This allows IQ test developers to establish norms, or standards, by which individual scores can be compared.
IQ testing has been controversial throughout history for a number of reasons, including:
- Discrimination: IQ tests have been used to justify eugenicist movements and discrimination against minority groups and disabled individuals.
- Validity: Not all experts agree on a standard definition of intelligence, so not all IQ tests measure the same things.
- Reliability: There is also the question of how reliable these tests are. Reliable IQ tests should provide consistent results. People should score roughly the same each time they take the test.
Many factors can influence IQ and scores can change over time. Some of the factors that can impact a person’s IQ score include:
- Educational access and background4
- Overall health and medical conditions
While higher IQ scores are linked to increased health, academic performance, and overall well-being, these scores do not necessarily predict an individual’s success in life. It is important to remember that IQ tests are only one measure of intelligence.
Many experts suggest that other important elements contribute to intelligence, including social and emotional factors. Some experts even suggest that these social and emotional skills actually matter more than IQ when it comes to determining success in life.5
History of IQ Tests
French psychologist Alfred Binet was the first to develop a formal test of intelligence and a form of his original test is still in use today as the Stanford-Binet intelligence test. Later, psychologist Charles Spearman developed a concept of general intelligence, or a general mental ability to perform a wide variety of cognitive tasks.
Psychologist Robert Yerkes developed IQ tests for the U.S. Army during World War I to test army recruits. During the 1950s, David Wechsler developed IQ tests for use with children and adults. These tests remain popular today.
Kaufman A. IQ Testing 101. New York: Springer; 2010.
Stangor C. 10.1 Defining and Measuring Intelligence. Introduction to Psychology. Version 2.1. Published July 2014.
Deary IJ, Strand S, Smith P, Fernandez C. Intelligence and educational achievement. Intelligence. 2007;35:13–21. doi:10.1016/j.intell.2006.02.001
Brinch CN, Galloway TA. Schooling in adolescence raises IQ scores. Proc Natl Acad Sci U S A. 2012;109(2):425‐430. doi:10.1073/pnas.1106077109
Bartholomew D. Measuring Intelligence. Cambridge, UK: Cambridge University Press; 2004.
Breedlove, S.M. Principles of Psychology. Sunderland, MA: Sinauer Associates, Inc; 2015.