Parts of a Box-and-Whisker Plot
- The median is the middle number in a data set when the values are arranged in numerical order.
- Example: 10, 17, 22, 23, 25, 36, 38, 45, 52, 60, 67
In this data set, the median is 36.
The median, then, divides a data set into two parts, one with the lower values and one with the higher values. We can now find the medians of both of these parts.
- The median of the lower part is called the lower quartile. It is also called the 25th percentile.
- Example: 10, 17, 22, 23, 25
In our example, the lower quartile (or 25th percentile) is 22.
- The median of the upper part is called the upper quartile. It is also called the 75th percentile.
- Example: 38, 45, 52, 60, 67
In our example, the upper quartile (or 75th percentile) is 52.
- The upper extreme is the greatest number in a data set, and the lower extreme is the lowest number.
- Example: 10, 17, 22, 23, 25, 36, 38, 45, 52, 60, 67
In our example set, the lower extreme is 10, and the upper extreme is 67.
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These numbers (the median, lower quartile, upper quartile, lower extreme, and upper extreme) are plotted on a number scale in a box-and-whisker format.