*36*

A **histogram **is a type of chart that uses rectangular bars to represent frequencies. It’s a helpful way to visualize the distribution of data values.

This tutorial explains how to create and modify histograms in Stata.

**How to Create Histograms in Stata**

We’ll use a dataset called *auto *to illustrate how to create and modify histograms in Stata.

First, load the data by typing the following into the Command box:

use http://www.stata-press.com/data/r13/auto

We can get a quick look at the dataset by typing the following into the Command box:

summarize

We can see that there are 12 total variables in the dataset.

**Basic Histogram**

We can create a histogram for the variable *length *by using the **hist **command:

hist length

**Histogram with Frequencies**

By default, Stata displays the density on the y-axis. You can change the y-axis to display the actual frequencies by using the **freq **command:

hist length, freq

**Histogram with Percentages**

You can also change the y-axis to display percentages instead of frequencies by using the **percent **command:

hist length, percent

**Changing the Number of Bins**

When you use the **hist **function in Stata, it automatically tells you how many “bins” it used. For example, in the previous examples it always used 8 bins:

However, we can specify the exact number of bins by using the **bin() **command. For example, the following code tells Stata to use 16 bins instead of 8:

hist length, percent bin(16)

We can also tell Stata to use fewer bins:

hist length, percent bin(4)

Notice that the more bins you use, the more granularity you can see in the data.

**Adding a Normal Density to a Histogram**

You can add a normal density curve to a histogram by using the **normal **command:

hist length, normal

**How to Modify Histograms in Stata**

We can use several different commands to modify the appearance of the histograms.

**Adding a Title**

We can add a title to the plot using the **title() **command:

hist length, title(“Distribution of Length”)

**Adding a Subtitle**

We can also add a subtitle underneath the title using the **subtitle() **command:

hist length, title(“Distribution of Length”) subtitle(“n = 74 cars”)

**Adding a Comment**

We can also add a note or comment at the bottom of the graph by using the **note() **command:

hist length, note(“Source: 1978 Automobile Data”)