Box-and-Whisker+Plots

A box-and-whisker plot is a graphic representation of data distribution over a range. In other words, it shows how much of your data falls into each quarter of values from the lowest value to the highest value. You will plot essentially 5 points from each data set: the lowest and highest values (end points), the median and the median of the lower half and the median of the upper half. Please note: median (middle), not mean (average) values are used for this. Take a data set of 4, 5, 6, 6, 7, 9, 9, 10, 12, 12, 15. There are 11 values. The median value is the middle number (the first 9). The "median" of the lower half is the middle of the lower half (the first 6). The "median" of the upper half is the middle of the upper half (the first 12).

On a number line, draw a vertical line through the median value. On the same number line, make a rectangular box that stretches from the lower-half median to the upper-half median. Put a dot at the lowest value to make an end point, and draw a straight line to the low end of the box. Put a dot at the highest value to make an end point and draw a straight line to the high end of the box. These two lines are the "whiskers" on the box-and-whisker plot.

Each section of data (each whisker and each "half" of the box) represents one quartile of the data. This allows us to see not only the range of data, but how the data points are spaced throughout that range.

If you don't understand my instructions, this link looked pretty good: Jen's Box-and-Whisker Plot Instructions