< List of probability distributions

A **unimodal distribution** is any distribution with a single peak, cluster, or high point (i.e., global maximum). It comes from the Latin word *uni*– (“one”) and Middle French modal (“*measure*”).

More specifically, the probability density function (PDF), histogram, or other graph of the distribution has one distinct peak. For example, the PDF of the normal distribution is unimodal: it has one distinct peak.

The values rise at first, reach a maximum, then slowly decrease to resemble the top of an Arabian (one-humped) camel.

Another example is the t-distribution, which is thinner and shorter than the normal distribution:

## Unimodal distribution and skewness

Unimodal distributions do not need to be symmetric; they can be off-center (skewed).

Data that is both unimodal and symmetrical is usually described as “normal,” and this idea is an important assumption for many hypothesis tests in statistics. But a unimodal distribution doesn’t have to have one peak in the center: the distribution can be skewed.

For example, the peak can be to the left of center (in which case it is called a right-skewed distribution because the right tail is longer than the left) or to the right of center (called a left-skewed distribution).

Many other skewed distributions are unimodal, including:

If a distribution has two peaks, it’s called a bimodal distribution; three or more peaks and it’s a multimodal distribution.

## Video Overview

The following video by Prof.Essa gives a useful overview of the unimodal distribution:

## References

Skewed histogram. Audrius Meskauskas, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons