How to read a box plot
A box plot is a way to show a five number summary in a chart. The main part of the chart (the “box”) shows where the middle portion of the data is: the interquartile range. The ends of the box show the first quartile (the 25% mark) and the third quartile (the 75% mark). The far left of the chart (at the end of the left “whisker”) is the minimum and the far right is the maximum. The median is represented by a vertical bar in the center of the box. Box plots (sometimes called box and whiskers charts) aren’t used that much in statistics. However, they can be a useful tool for getting a quick summary of data.
How to read a box plot: Steps
Step 1: Find the minumum.
The minimum is the far left hand side of the graph, at the tip of the left whisker. For this graph, the left whisker end is at approximately 0.75.
Step 2:Find Q1.
Q1 is represented by the far left hand side of the box. In this case, about 2.5.
Step 3: Find the median.
The median is represented by the vertical bar. In this boxplot, it can be found at about 6.5.
Step 4: Find Q3.
Q3 is the far right hand edge of the box, at about 12 in this graph.
Step 5: Find the maximum.
The maximum is the end of the “whiskers”: in this graph, at approximately 16.
All done. That’s how to read a box plot!
Still have questions? Ask on our statistics forums. Our stats guy will be happy to answer your questions.
Check out our YouTube channel for lots of videos on basic statistics, including using Excel to draw graphs and charts. New videos being added every week; Comments and suggestions are always welcome.