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 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.
That’s how to find a boxplot interquartile range!
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