Scientists Say: Outlier

This is a data point that falls outside a normal range

Giraffes are tall, right? Well, once in a while, a small giraffe is born. These giraffes are outliers — data points that fall outside the normal range.

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Outlier (noun, “OUT-lie-er”)

This is an observation or data point that falls outside of a normal range. In scientific studies, an outlier may differ a great deal from other data points that the scientist has taken. Sometimes, scientists take out outliers from their data sets.

Outliers can also occur in the real world. For example, the average giraffe is 4.8 meters (16 feet) tall. Most giraffes will be around that height, though they might be a bit taller or shorter. But recently, scientists found a giraffe that was only about 2.7 meters (9 feet) tall, and another that was a tiny 2.6 meters (8.5 feet). These two teensy giraffes are outliers.

Outliers can occur by accident. Sometimes, a scientist makes a mistake or writes down a number wrong. Outliers could also mean there’s a flaw in the way the scientist is testing their hypothesis. So it’s important to understand outliers before throwing them out.

But sometimes, an outlier is just unusual or rare. That doesn’t mean it’s wrong. A short giraffe can be just a short giraffe.

In a sentence

When scientists check if voting districts are fair, it’s important to look for outliers.

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Bethany Brookshire was a longtime staff writer at Science News for Students. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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