How do you use a box and whisker plot?

Answer 1

Box and whisker plots are used to give a visual indication of where quartiles and highest/lowest values fall, so they're useful for visually comparing various sets of data.

The "whisker" on the left extends to the lowest value in the data range (the left-most point). The first edge of the "box" indicates the lower quartile, the middle line in the box represents the median quartile, and the upper edge of the box represents the 3rd quartile. The "whisker" on the right extends to the highest value in the data set. Clearly when using many box and whisker plots, and comparing them to each other, it helps greatly if you use the same scale on each plot.

Sometimes it may be decided that your lowest/highest data values are "outliers" (anomalous results), in which case they are still included in the box and whisker plot, but they should be demarcated by a hollow circle wherever the outlier is deemed to be.