Human Diversity and IQ Distribution

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  • 0:02 Intelligence
  • 1:31 IQ
  • 2:34 Mental Age
  • 3:38 Bell Curve Distribution
  • 6:18 Lesson Summary
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Lesson Transcript
Instructor: Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

People vary widely in their talents and skills. Some people are very good at schoolwork, which is often reflected in their IQ scores. Watch this lesson to find out more about IQ scores, including mental age and the bell curve distribution.


Claire has always been a bright girl. She understands things really quickly and does really well in school. Recently, she and her classmates took an IQ test at school, and Claire got a 115. But her parents wonder what that means. Is she a genius or just average?

Intelligence is defined in many different ways. Often, it is related to problem-solving and thinking skills. For example, if you give Claire a riddle, she can almost always figure it out. Some psychologists stress that there are multiple different intelligences, like the ability to get along well with others or the ability to understand and control one's own body.

But for the purposes of intelligence testing, or measuring one's intelligence through an assessment, intelligence is usually defined as a propensity for scholarship. In other words, most intelligence tests measure how well a person is likely to do in school. Because it is about scholastic aptitude, intelligence testing is not usually applicable to adults.

For example, if Claire does really well on an intelligence test, it would mean that she was likely to do really well in school. If she did not-so-well on the intelligence test, then she'd probably do not-so-well in school. Let's look closer at IQ, what an IQ score means, and how different people have different scores.


Remember that Claire has an IQ of 115. But, what does that mean? What is IQ, and is a score of 115 really, really good or really, really bad?

IQ stands for intelligence quotient, which is a score based on an intelligence test. Remember that we said that intelligence tests measure how well a person is likely to do in school, so that's what a person's IQ measures: his or her ability to get good grades in subjects like English and math.

The average IQ score is 100, which means that Claire is above average. That's great news! But, does that also mean that she's a better person than other kids, or that she's better at everything?

No! Remember that some psychologists believe that there are multiple intelligences, like interpersonal, kinesthetic, or musical intelligence. All an IQ can tell Claire and her parents is that she is above average in her ability to do well in school.

Mental Age

Sometimes, people talk about a person's mental age, or a person's ability expressed as the age at which most people reach that ability. If that sounds confusing, think about it like this: if Claire answers a bunch of questions that are commonly answered correctly by 10-year-olds, then her mental age is ten.

If Claire was born ten years ago, having a mental age of ten means that she's average. But if her chronological age, or the number of years a person has lived, is only eight, then she's two years ahead of where she is expected to be; that is, her chronological age is eight, but her mental age is ten. That's a good thing!

Of course, the opposite could be true, too. If Claire isn't very good in school, she might score low on an IQ test. Then, her mental age might be six. Her chronological age hasn't changed; she's still lived for eight years. But her mental age is now lower than her chronological age, indicating that she might struggle in school.

Bell Curve Distribution

All that mental age stuff is nice and all, but Claire's parents what to know what her IQ of 115 means in terms of other people. Is their daughter a genius or not so smart after all?

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