7.3. Box-and-Whisker Plots http://www.ck12.org
The three medians divide the data into four equal parts. In other words:
- One-quarter of the data values are located between 6 and 9
- One-quarter of the data values are located between 9 and 13
- One-quarter of the data values are located between 13 and 15
- One-quarter of the data values are located between 15 and 21
From the box-whisker, any outliers (unusual data values that can be either low or high) can be easily seen on a box
plot. An outlier would create a whisker that would be very long.
The next diagram will show where these numbers are actually located on the box-and-whisker plot.
Each whisker contains 25% of the data and the remaining 50% of the data is contained within the box. It is easy to
see the range of the values as well as how these values are distributed around the middle value. The smaller the box,
the more consistent the data values are with the median of the data.
Example 2:
After one month of growing, the heights of 30 parsley seed plants were measured and recorded. The measurements
(in inches) are shown in the table below.
TABLE7.14: Heights of Parsley (in.)
6 26 23 33 11 26
22 28 30 40 38 18
11 37 12 34 49 17
25 37 46 39 8 27
16 38 18 23 26 14Construct a box-and-whisker plot to represent the data.
The data organized from smallest to largest is shown in the table below. (You could use your calculator to quickly
sort these values)
TABLE7.15: Heights of Parsley (in.)
6 8 11 11 12 14
16 17 18 18 22 23
23 25 26 26 26 27
28 30 33 34 37 37
38 38 39 40 46 49