Interpretation of an IQ Score

Dr. Russell T. Warne

Sep 10, 2023

IQ scores get a lot of attention, but there people unfamiliar with IQ tests often do not know how to interpret them. That’s because IQ scores are not like school test scores. (If someone obtains an IQ score of 80, that does not mean that the person answered 80% of questions correctly!) This is a simple guide to help examinees understand IQ scores.

Characteristics of IQ

When graphed, IQ scores generally form a shape called a “normal distribution” (also informally called a “bell curve”), where the average is in the middle, and most examinees’ scores are near the middle. The further from the average a score is, the fewer people obtain that score. A picture of a normal distribution is shown below.

Most IQ tests have a scale that sets the average at 100 and a standard deviation of 15. (The standard deviation is a measure of how much scores are spread out from the average.) This means that 68% of the population has an IQ between 85 and 115 (that is, plus or minus 15 points from the average). 95% of the population has an IQ between 70 and 130, and almost everyone (99.73%) has an IQ between 55 and 145. In theory, IQ scores do not have a minimum or maximum, but functionally, there is little need for most IQ tests to measure IQ beyond 150 or so.

There is an important implication of using the normal distribution to interpret IQs: it means that IQ score is a relative measure of intelligence, not an absolute one. In other words, scores take their meaning from how well a person performs, compared to others from their same age group.

IQ score ranges

For over 100 years, IQ test creators have proposed labels for ranges of IQ scores, and these are changed periodically. The table below displays the traditional labels for different IQ ranges and the current labels for the Wechsler tests:

The change shown in the table is a good illustration of how the labels are arbitrary. The same is true with cutoffs for the ranges. In the past, other systems used different cutoffs and labels, such as “gifted” or “disabled.” Regardless of the system used, it is important to understand that it is the score receiving the label -- not the person.

What does my IQ score mean?

The score ranges and labels are helpful, but they are just a starting point. A reputable test will provide a detailed score report for examinees that help them gain an in-depth understanding of their IQ score and the other scores that a good test provides. If the IQ test is administered individually by a psychologist or clinician, then the examinee can realistically expect a verbal explanation and a chance to ask questions.

It is helpful to remember a few principles, though:

• The average IQ score is 100.

• About 2/3 of people have scores between 85 and 115. (Scoring within this range is typical.)

• 95% of people have scores between 70 and 130.

• A score of about 70 to 75 is the cutoff for an intellectual disability. Below this threshold, people have difficulty living independently.

• The minimum IQ for obtaining stable employment and functioning well in society is about 80 to 85.

• Professional jobs that require advanced education almost always have a minimum IQ of 110.

Higher scores are, generally, associated with better life outcomes.

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