Histograms

Definition of a Histogram

• A Histogram displays a range of values of a variable that have been broken into groups or intervals.

• Histograms are useful if you are trying to graph a large set of quantitative data

• To make a Histogram, you divide the range of data into intervals of equal length, count the number of observations in each interval, and represent each interval with a bar indicating the number of observations.

Disenfranchisement Rates for all 50 States

0 8.1 24.9 6.6 9.2

1.5 17.1 3.9 14 11.3

2.8 1.2 4.6 2.8 16.1

3.1 3 10.3 5 17.4

7.2 4 2.4 7.9 24.7

14.2 8.3 4 14.3 0

16 18.9 5.7 2.8 0.8

0.7 3.5 12.9 6.2 1.5

2.8 4.2 2.6 8.3 1.5

3.7 9.2 4.2 8.4 2.6

Step 1: Sort the Data from Lowest to Highest

0 2.6 4 7.9 14

0 2.8 4 8.1 14.2

0.7 2.8 4.2 8.3 14.3

0.8 2.8 4.2 8.3 16

1.2 2.8 4.6 8.4 16.1

1.5 3 5 9.2 17.1

1.5 3.1 5.7 9.2 17.4

1.5 3.5 6.2 10.3 18.9

2.4 3.7 6.6 11.3 24.7

2.6 3.9 7.2 12.9 24.9

Step 2: Determine how many groups of data you want to have.

Step 3: Determine the approximate range of the set of data

Step 4: From Steps 2 and 3, determine the range of each individual group

For example, we’ll use 5 groups

0% through 24.9% (approximately 25%)

I decided to have 5 groups. The range is from 0% - 25%. 25% divided by 5 is 5%. So each group should have a range of 5%.

Step 5: Make a list of the groups you will be using.

Step 6: Using your data, count how many numbers fall into each group

Group 1: 0% - 5%Group 2: 5% - 10%Group 3: 10% - 15%Group 4: 15% - 20%Group 5: 20% - 25%

Group 1: 0% - 4.99%Group 2: 5% - 9.99%Group 3: 10% - 14.99%Group 4: 15% - 19.99%Group 5: 20% - 25%

2512652

Step 7: graph each group

25

12

65

2