Representing categorical data in a bar graph means matching each category to a bar whose height or length shows its whole-number frequency, using a clearly labeled, evenly spaced scale that may count by 1s, 2s, 5s, or 10s. The graph preserves the data’s quantities for comparison and interpretation; bars represent separate categories rather than continuous intervals, and histograms, relative-frequency graphs, and more complex multivariable displays are not included.
First, organize the data into categories and their frequencies. A frequency tells how many times each category occurs.
Suppose 15 students were asked about their favorite fruit:
| Fruit | Number of students |
|---|---|
| Apples | 6 |
| Bananas | 4 |
| Grapes | 3 |
| Oranges | 2 |
For this example, we can make a horizontal bar graph:
The greatest frequency is , so use a scale from to , counting by s:
The spaces between numbers must be equal.
Make each bar end at its category’s frequency:
Favorite Fruits
Number of students
0 1 2 3 4 5 6
|----|----|----|----|----|----|
Apples ██████████████████████████████ 6
Bananas████████████████ 4
Grapes █████████████ 3
Oranges████████ 2
Each bar begins at and reaches the correct number. There is space between categories because fruits are separate categories, not parts of one continuous scale.
The graph shows that apples were the most popular fruit and oranges were the least popular fruit.
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