Drawing a bar graph for grouped data
Here is the data for the ages of customers shopping in the Bitesize CD store.
| Ages of customers in 1-hour period | 25, 29, 45, 19, 36, 17, 60, 51, 39, 24, 15, 13, 31, 18, 24, 32, 37, 27, 23, 53, 41, 34, 29, 28, 52, 17, 55, 47, 34, 28, 22, 20, 64, 39, 38, 33, 24, 16, 27, 19, 26, 27, 25, 32, 26, 48, 54, 35 |
| Ages of customers in 1-hour period |
|---|
| 25, 29, 45, 19, 36, 17, 60, 51, 39, 24, 15, 13, 31, 18, 24, 32, 37, 27, 23, 53, 41, 34, 29, 28, 52, 17, 55, 47, 34, 28, 22, 20, 64, 39, 38, 33, 24, 16, 27, 19, 26, 27, 25, 32, 26, 48, 54, 35 |
We could show this data in a bar chart, but it would have a lot of bars!
We can group them together so that we have fewer categories.
When choosing intervals for the data sets make sure that they do not overlap and that they include all the data.
For example, you could use the following intervals to draw a frequency diagram.
- 1 - 20
- 21 - 30
- 31 - 40
- 41 - 50
- 51 - 60
- 61 - 70
This is the same set of data put into groups:
| Age | Number of people |
| 1 - 20 | 9 |
| 21 - 30 | 16 |
| 31 - 40 | 12 |
| 41 - 50 | 4 |
| 51 - 60 | 6 |
| 61 - 70 | 1 |
| Age | 1 - 20 |
|---|---|
| Number of people | 9 |
| Age | 21 - 30 |
|---|---|
| Number of people | 16 |
| Age | 31 - 40 |
|---|---|
| Number of people | 12 |
| Age | 41 - 50 |
|---|---|
| Number of people | 4 |
| Age | 51 - 60 |
|---|---|
| Number of people | 6 |
| Age | 61 - 70 |
|---|---|
| Number of people | 1 |
We can now put the data into a bar graph.