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Finding an interquartile range on a boxplot is easy! (If you only have numbers, see How to find an interquartile range from a set of numbers). This how-to will show you how to find an interquartile range in a couple of easy steps.
Let’s find the interquartile range for the above graph.
- Step 1: Find Q1.Q1 is represented on a boxplot by the left hand edge of the “box”.
In the above graph, Q1 is approximately 2.5. (If you are interested, a better explanation of what Q1 is can be found in this article on finding the five number summary.)
- Step 2: Find Q3.
Q3 is represented on a boxplot by the right hand edge of the “box”.
Q3 is approximately 12 in this graph.
- Step 3: Subtract the number you found in step 1 from the number you found in step 3.
This will give you the interquartile range. 12 – 2.5 = 9.5.