How a Normative Group Works in Psychology

Being in the 99th Percentile

Students Studying
Dan Kitwood / Staff / Getty Images

You usually hear the term normative group, or norm group, in discussions of tests and measures. It refers to the sample of test takers who are representative of the population for whom the test is intended. That normative group is supposed to stand for a hypothetical "typical" test taker, one who represents the group that's being tested.

How Norm Groups Are Used in Psychological Testing

When designing a test of something, whether it's academic ability or signs of depression, it's important for the people making the test to understand the group that they are testing and to know what would be considered normal within that group.

So for instance, the SATs are a standardized test of academic potential. It is taken by high school juniors and seniors around the United States. Therefore, the normative group for the SATs would be a randomized, cross-cultural group of American junior and high school students who accurately reflect the diversity (and therefore the average) of that group of test takers.

In psychology, the normative group for a test to diagnose depression in 5- to 10-year-olds in the United States would be a sample of 5- to 10-year-olds from various demographic groups in the United States.

How Norm-Referenced Tests Are Assessed

Norm-referenced tests are assessed differently than criterion-referenced tests. Criterion-referenced tests are the typical format of tests you'd find in school. Questions have right answers and wrong answers and your scores are graded out of a perfect score.

By contrast, it's not possible to "pass" or "fail" a norm-referenced test. Rather, it will give you results based on your performance compared to a normative group.

Take, for instance, an IQ test, one of the main types of norm-referenced tests. 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 percent) on the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) tend to lie between plus 15 or minus 15 points from the average score of 100.

This means that approximately 68 percent of people who take this test will score somewhere between 85 and 115.

Percentiles as an Expression of Performance

You may also see results of norm-referenced tests presented as a percentile. These percentiles are based on a bell curve, with the "norm" falling in the middle of the curve, and then ranges of percentiles are demarcated as deviations from the norm (either above or below the curve). If you've taken a standardized test such as the SAT, you may have noticed that you got both a score that was a number based off of the total number of points you could have received, but that number was also translated into a percentile that reflected how you did in relation to other test takers.

The further away from the norm, you are, the further away from the 50th percentile your score will be. So, for instance, an SAT score in the 99th percentile means you scored better than 99 percent of other test takers.