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Unimodal vs. Bimodal Distribution

Unimodal vs. Bimodal Distribution

Description:

This lesson will explain distributions with one or more modes.

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Tutorial

What's Covered

In this tutorial, you're going to learn about unimodal distributions versus bimodal distributions. This will cover:

  1. Unimodal distribution
  2. Bimodal distribution
  3. Multimodal distribution

1. Unimodal distribution

Oftentimes distributions will have a clear peak to their shape. They will peak in just one place on the distribution:

  • This distribution has a peak in the center.

  • This distribution peaks further to the right.

  • This distribution peaks further to the left.

They all have a clear peak, so all of these are called a unimodal distributions.

Term to Know

  • Unimodal/Single-Peaked Distribution
  • A distribution where one value or bin contains more data than the other values or bins.

The tallest bar is called the mode.


2. Bimodal distribution

You might have a distribution that will have two distinct regions with lots of data points, and a gap in the middle. When this happens, the two peaks form on the distribution. And those are both called modes.

A distribution like this is called bimodal.

Term to Know

  • Bimodal Distribution
  • A distribution where there are two distinct values or bins that contain more data than the others, usually separated by a gap.

Technically, there's only one bin that's the mode: the tallest one. But in the above graph, there are two bins that are the tallest relative to the others around them. So they're sort of local modes.

Now sometimes you have a distribution that appears bimodal:

It appears to be bimodal, but upon further examination of heights, it's possible that you have two different distributions that happened to be graphed on the same set of axes:

There might be some hidden variable that causes the bi-modality. When viewed separately, you end up with two unimodal distributions. They just happened to be graphed on the same set of axes.


3. Multimodal distribution

Any distribution with more than two peaks is called multimodal.

Term to Know

  • Multimodal Distribution
  • A distribution where there are many values or bins that contain more data than other nearby bins, usually separated by gaps.

This distribution, for instance, has four peaks:

You can have the same issues with thes, as you did with the bimodal distribution, in that it may be multiple distributions graphed on the same set of axes.

Big Idea

Uni means one, Bi means two, and modal means the number of modes each distribution has.


Summary

S distributions are unimodal, or single peaked distributions. Others are bimodal, which means they are clearly double-peaked, and some are multimodal. Sometimes, a bimodal distribution is simply two unimodal distributions graphed together. Oftentimes, there's a reason for the bi-modality.

Thank you and good luck.

Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR JONATHAN OSTERS

TERMS TO KNOW
  • Unimodal/Single-Peaked Distribution

    A distribution where one value or bin contains more data than the other values or bins.

  • Bimodal Distribution

    A distribution where there are two distinct values or bins that contain more data than the others, usually separated by a gap.

  • Multimodal Distribution

    A distribution where there are many values or bins that contain more data than other nearby bins, usually separated by gaps.