In the search box at the upper left hand corner of the site, type in 2-7b Box and whisker plots. This will bring you to another post with YouTube videos explaining how to construct box and whisker plots. Another way to find this post is to click on the July 1st, 2008 calendar date on the upper right hand side of the blog.
1. Order numbers from least to greatest.
2. Find the median.
3. Mark the median on a number line drawn with equal intervals (count by same amount, 1’s or 2’s or 5’s or 10’s or 20’s or 100’s, etc. all the way across).
4. Mark lower extreme (the smallest number) on the number line.
5. Mark upper extreme (the largest number on the number line.
6. Find the median of the lower half of numbers (call this median the “lower quartile”.
7. Mark lower quartile on the number line.
8. Find the median of the upper half of numbers (call this median the “upper quartile”.
9. Mark upper quartile on the number line.
10. Draw a box from the lower quartile to the upper quartile. Divide the box into two at the median.
11. Draw line from lower extreme to lower quartile.
12. Draw line from upper quartile to upper extreme.
NOTE: To find outliers:
1. Find the interquartile range.
The interquartile range = upper quartile – lower quartile.
2. Multiply the interquartile range x 1.5
3. Add the answer from step #2 to the upper quartile number. Any number above the answer to step # 3 is an outlier and should not be included in the box and whisker plot.
4. Subtract the answer from step # 2 from the lower quartile number. Any number below the answer to step #4 is an outlier and should not be included in the box and whisker plot.
