Box Plot interquartile range: Overview
The interquartile range(IQR) is a measure of spread in statistics. the mean (average) tells you where the center of data is; the IQR tells you where the average set of numbers is — the set of numbers in the middle. This can give you a better idea of where the middle set of scores are, and that’s why it’s sometimes called the middle fifty. It excludes high scores (the top 25%) and the bottom scores (the bottom 25%).
A boxplot is a type of graph in statistics. It’s sometimes called a box and whiskers chart, because there is a central box and two lines emitting from the left and right that look like whiskers. A box plot gives you a five number summary — the mean, the minimum, the maximum, the first quartile (25%) and the third quartile (75%).
This how-to will show you how to find a box plot interquartile range in a couple of easy steps.
Watch the video or read the steps below:
Box Plot interquartile range: How to find it
Sample question: Find the interquartile range for the above box plot.
- Step 1: Find Q1.Q1 is represented on a boxplot by the left hand edge of the “box” (at the point where the whisker stops).
In the above graph, Q1 is approximately at 2.6. If you are interested, a complete explanation of what Q1 is here: 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 – 2.6 = 9.4.
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