Ideas
Box plots
Box plots (also known as box-and-whisker plots) are a way of showing the five-number summary for a data set. The five number summary consists of the following five statistics:
| Minimum | 17 |
|---|---|
| Lower quartile | 52 |
| Median | 69 |
| Upper quartile | 87 |
| Maximum | 100 |
The box plot below shows a nice summary of all this information:
As you can see the box plot consists of a number line, a rectangle with a line inside (the box), and 2 horizontal lines (the whiskers). The box represents the middle 50\% of the scores and its size tells us the interquartile range.
25\% of the scores lie between each quartile. So for this example, 25\% of the scores would lie between 17 and 52, 52 and 69, 69 and 87, and 87 and 100.
To find the percentage of scores between 52 and 100, we would multiply 25\% by 3 since there are 3 quartiles in this range: 3\times 25\%=75\%.
Examples
Example 1
Create a box plot to represent the data in the table below.
| Minimum | 10 |
|---|---|
| Lower quartile | 20 |
| Median | 40 |
| Upper quartile | 55 |
| Maximum | 75 |
Box plots are a graphical representation showing the five-number summary for a data set.