# Unimodal Distribution in Statistics

Descriptive Statistics > Unimodal Distribution

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## Unimodal Distribution : Overview

A unimodal distribution is a distribution with one clear peak or most frequent value. The values increase at first, rising to a single peak where they then decrease. The “mode” in “unimodal” doesn’t refer to the most frequent number in a data set — it refers to the local maximum in a chart. Technically there are the same thing: one mode (one common number) will equal one peak in a graph. However, when you are looking at a graph and trying to decide if it’s a unimodal distribution or not, there’s no list of numbers to guide you.

The normal distribution is an example of a unimodal distribution; The normal curve has one local maximum (peak).

A normal distribution curve, sometimes called a bell curve.

Other types of distributions in statistics that have unimodal distributions are:

In elementary statistics, you probably will see the first three types of distribution listed above, but not the Cauchy. The Cauchy is a particular type of distribution where the expected value does not exist. See here for more information on the Cauchy distribution.

The uniform distribution is a type of probability distribution where the odds of getting any number within the range are the same. For example, if you roll a die, your odds of rolling any number (1,2,3,4,5,6) are the same.

Image courtesy of the University of Houston.

### Bimodal Distribution

“Bi” means two, so there are two local maximums (peaks) in a bimodal distribution.

### Symmetry and the Unimodal Distribution

Unimodal distributions aren’t necessarily symmetric like the normal distribution. They can be asymmetric, or they could be a skewed distribution.

## Other types of distributions

Multimodal distributions, where there are more than two peaks, are very rare. One example of a multimodal distribution is a trimodal distribution, which has three peaks.

Multimodal distribution with many modes, or peaks. Image credit: USDOT

U distributions have a distribution in the shape of the letter U, with large frequencies at the left and right of the distribution and few values in the middle.

Fun fact: The mean, median and mode often occur in alphabetical order (or reverse alphabetical order) on unimodal distributions.

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