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What is IQ? - Tests, Definition & Quiz

Instructor: Devin Kowalczyk

Devin has taught Psychology and has a master's degree in Clinical Forensic Psychology, and will earn a PhD in 2015.

What is IQ and how do professionals determine what your IQ is? What does it mean to have a high or low IQ score, and can you be skilled in one area or is intelligence very broad? Does mayonnaise have an IQ?

We also recommend watching Methods of Measuring Intelligence: Interpreting IQ Scores & Score Range and Two Types of Intelligence: Fluid and Crystallized Intelligence

What is IQ?

Have you ever wondered how smart you are compared to the people in your life, or even compared to all people your age? You can get a good idea of your intelligence level by determining your IQ. An IQ, or intelligence quotient, is a score you receive on a test that assesses intelligence. But what exactly are these tests?

We will begin with an example of an IQ test, and then explain the different components and what they mean. Following this, we will look at the various tests used to assess IQ and examine some of their differences.

Filbert Humperdinck

Mr. Humperdinck, a 26-year-old man, decides he wants to have his IQ tested. He goes to a licensed clinician - often a doctoral-level psychologist or psychiatrist or a masters-level psychologist with special training - and says he wants to be tested.

The clinician, Dr. Noberson, sits Mr. Humperdinck down and they complete a series of tests. This is a representative example of the type of subtests:

  • Assorting simple blocks to match an image
  • Remembering numbers and repeating them back in varying orders
  • Defining words
  • Filling out a problems sheet as quickly as possible

Mr. Humperdinck finishes many more tests similar to these, and Dr. Noberson says he will have the results by next week.

Mr. Humperdinck returns and is told he has a Full Scale IQ of 100. His Verbal Comprehension is 110, his Perceptual Reasoning is 90, his Processing Speed is 120, and his Working Memory is 80. Mr. Humperdinck nods along, completely bewildered by what Dr. Noberson is saying. So what do these scores even mean?

IQ Math!

IQ is a comparison of your test results to the results of people your own age. The average IQ is 100. If you gave 1,000 people a really hard test, your results would look like this:

Bell Curve

The higher the graph goes, the more people who have achieved that score. As you can see from the graph above, there is a bell shaped distribution. Most people are in the center, but some people score really well and some people score really poorly. By having the IQ average at 100, scores can go high or low and still make sense because of their relationship to 100.

The different colors of the above graph are standard deviations. Standard deviation is a mathematical way of grouping people together. If you look at the red line on 100, the blue group to your right is considered one positive standard deviation. In that blue group is 34.1% of the population. If you combine it with the green group just to the left of the red line, you have everything within one standard deviation of the average (average is 100), or 68.2% of the population (1 standard deviation= 34.1%; by combining both above and below the standard deviation you get 68.2%). Standard deviations allow for easy groupings and predictions.


What does all this mean? A standard deviation in IQ points is 15, so 68.2% of the population will have scores between 85 and 115. This is labeled an Average IQ, or a name for a group of people scoring around the average score. This name for a group helps makes it easier to group test takers together.

About 95.4% of the population will have an IQ score between 70 and 130, which is everyone within two standard deviations. Scores that are between 70 and 85 may be labeled Below Average while scores between 115 to 130 could be labeled Above Average.

IQ Meaning

Put simply: intelligence is mental horsepower. If you have more horsepower you can do more, faster. If you have less horsepower you can probably do as much, but it will take more time and energy. An IQ is a quick way to reference this.

When you take an IQ test, you are compared to people who have taken the test before. Prior to the release of the test, the writers of the IQ test had several hundred, sometimes more than a thousand, people assessed. These people create the bell-shaped curve we see above and the scores to which Mr. Humperdinck will be compared.

When you take one of the subtests, or one of the smaller tests that make up the IQ test, (the bullet points above), the amount of right versus wrong you score is compared to other people your age. These subtests are often combined to give you Specific Scales, such as Verbal, Perceptual, etc. These specific scales are then combined into a Full Scale, meaning this is your overall IQ.

  • IQ Test= All subtests in a set made by a group of researchers
  • Subtest= specific test; see bullets above
  • Similar subtests combined = Specific Scale (Word definitions + Synonyms= Verbal)
  • All Specific Scales combined = Full Scale IQ

If you do as well as everyone else, meaning your abilities are similar to people your age, then you receive a score of 100. If you score higher than others your age, you receive a score higher (>100), and if you score lower, then you get a lower score (<100).

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