12-4 Box-and-Whisker Plots

Objectives

To make and interpret box-and-whisker plots

To find quartiles and percentiles

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In the Solve It, you may have looked at different parts of each data set in order to compare the two data sets.

Essential Understanding Separating data into subsets is a useful way to summarize and compare data sets.

Quartiles are values that divide a data set into four equal parts. The median (or second quartile, Q 2 cap q sub 2 ) separates the data into upper and lower halves. The first quartile ( Q 1 ) open , cap q sub 1 , close  is the median of the lower half of the data. The third quartile ( Q 3 ) open , cap q sub 3 , close  is the median of the upper half of the data. The interquartile range is the difference between the third and first quartiles.

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For a set of data that has an odd number of values, you do not include the median in either half when finding the first and third quartiles.

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