Allows the comparison of your score on a test to the scores of others.

Tests of intellectual functioning (IQ)

Tests of intellectual functioning are designed to measure different mental abilities. These tests are commonly called IQ tests. IQ tests measure the following mental abilities:

• reasoning;
• problem solving;
• abstract thinking;
• judgment;
• academic learning;
• experiential learning

Previously an IQ score of 70 or below was the recommended cutoff score. The DSM-5 (APA, 2013) has de-emphasized specific IQ scores. Nonetheless, an assessment of intellectual functioning remains central to diagnosis. Thus, IQ scores are still very important considerations. Therefore, it's useful to understand what IQ scores mean.

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If everyone took an IQ test there would be a wide variation in scores. This is called a distribution of scores. The average score (the mean) is the score that is the smallest distance away from all the other scores in the distribution.

When naturally occurring attributes such as IQ (or hat size, for that matter) are measured, the distribution looks like inverted 'U' shape curve. This curve is called the normal curve. Normal curves have special properties. The area under the normal curve represents the chances of observing a certain score. Then we know how common or uncommon a certain score is.

IQ test scores are standardized. Standardized tests allow a person's score to be compared to other people. IQ tests have a mean score of 100 and a standard deviation of 15. Standard deviation can be understood as the shape of a curve. Some U shaped curves are low, flat, and wide. Other U shaped curves are high, tight, and narrow. Mathematically, standard deviation is a specific distance from the mean. Standard deviation describes this distance and thus the shape of the curve.

Because of mathematical qualities of normal curves, we know that 68% of the area under the normal curve is one standard deviation above and below the mean. Therefore, IQ scores falling between 85 and 115 are common. About 68% of the population would score in that range. About 95% percent of the area under the normal curve occurs between two standard deviations. Therefore, IQ scores falling between 70 and 130 occur 95% of the time. There is a remaining 5%. Half or 2.5% will be above a score of 130. The other 2.5% will be below a score of 70. Therefore, we would expect that only 2.5% of the population would score above 130. This group represents people with an unusually high IQ. They are often termed, "gifted." We would also expect that only 2.5% of the population would score below 70. Historically, scores below 70 indicated an intellectual disability.

IQ tests have two parts. One part measures verbal abilities. The other part measures spatial abilities. Spatial is sometimes called performance skills. It refers to movement and the manipulation of three-dimensional space. Verbal and spatial scores vary widely. One person might have low scores across the board. Another person might do well verbal IQ but poorly on spatial IQ. Therefore, even though two people have the same total IQ scores, their abilities may be very different.

While many tests utilize similar methods to derive their scores, it is also important to note that each IQ test is different. Additionally, scoring methods may not be the same from one test to another.

IQ Definition

IQ is short for intelligence quotient and is "a type of standard score that indicates how far above, or how far below, his/her peer group an individual stands in mental ability" according to Mensa International, an organization for people scoring in the top 2% for IQ.

Types of IQ Tests

There are several different intelligence tests in existence and their content can vary considerably. Some are used for 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

Which IQ test is best or more accurate? Unfortunately, there is no consensus on this. Instead, some suggest that each test measures a different notion of intelligence, thus IQ test scores can vary depending on what is being measured and the test being taken.

Uses of IQ Tests

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 Testing

IQ can have an impact on different areas of 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.

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.

IQ ClassificationsIQ LevelDescriptive Classification130+Very Superior120 to 129Superior110 to 119High Average90 to 109Average80 to 89Low Average70 to 79Borderline69 & belowIntellectual DisabilityThese 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, or a bell-shaped curve in which most scores lie near or around the average IQ test score. For example, the majority of scores (about 68%) on the Wechsler IQ 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 IQ 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.

In many cases, an IQ test score that falls below 70 is considered low IQ, while a score of above 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 as diagnosticians also consider factors such as the age of onset and adaptive skills.

How common are very high IQ test 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 an IQ test.

How to Interpret Your IQ Test Score

To understand what your IQ test score really means, it can be helpful to know how these tests are designed and how your score compares to others. Your score on an IQ test can tell you how you compare to others in your peer group regarding:

• Language skills
• Mathematical abilities
• Memory
• Processing speed
• Reasoning abilities
• Visual-spatial processing

To adequately assess and interpret IQ test scores, scientists who develop these tests use a process known as standardization. This involves administering the test to a representative sample of the population that will eventually take the test.

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.

How to Find the Mean, Median, and Mode

Potential Pitfalls of IQ Tests

IQ testing has been controversial throughout history for a few 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. Put another way, people should score roughly the same each time they take the test.

While higher IQ test 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.

Factors Affecting IQ Test Scores

Many factors can influence IQ and scores can change over time. Some of the factors that can impact a person's IQ test score include:

• Educational access and background
• Nutrition
• Culture
• Environment
• Overall health and medical conditions

What Factors Influence IQ

Many experts believe 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. 

History of IQ Tests

French psychologist Alfred Binet was the first to develop a formal test of intelligence and a form of his original IQ test is still in use today as the Stanford-Binet Intelligence Test. Later, psychologist Charles Spearman developed a concept of general intelligence, or 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.

Alfred Binet and the History of IQ Testing

Where to Find an IQ Test

If you want to take a formal IQ test, a licensed psychologist can provide this service for you. This mental health professional is trained to administer and supervise IQ tests, also ensuring that the test used is valid and reliable.

Several online sites also offer free IQ tests if you're more interested in knowing how you score but don't need a formal test. When selecting a free IQ test provider, it can be helpful to choose an organization that is reputable in the field of intelligence. For example, Mensa International offers a free online IQ test.

A Word From Verywell

While IQ test scores can reveal information about an individual's abilities in certain domains, it is important to remember that other factors—including such things as adaptive skills, emotional intelligence, and task performance—are also important indicators of an individual's capabilities.

Which intelligence score takes a person's mental and chronological age into account?

What tests rate mental abilities such as reasoning and problem solving?

What kind of test measures a person's level of knowledge in a given subject area?

Who was responsible for the first standardized IQ test?