11.2 Box-and-Whisker Plots
Box-and-Whisker Plots
A box-and-whisker plot is a data display that organizes data values into four groups:
Lower quartile: the median of the lower half
Upper quartile: the median of the upper half
Lower extreme: the least data value
Upper extreme: the highest data value
Interquartile range: the difference between the upper quartile and lower quartile
How to make a box-and-whisker plot:
A. Organize the data:
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5)
Order the data from least to greatest
Find the median of all the values
Find the lower quartile; the median of the data values to the LEFT of the original median
Find the upper quartile; the median of the data values to the RIGHT of original median
Identify the extremes; the least and highest data values
*When a data set has an odd number of values do NOT include the median in either half of the
data when determining quartiles.
B. Plot the data above or below a number line:
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Draw a number line that includes all the numbers in your data
Mark the median, upper and lower quartile with tick marks
Draw a box around the 3 tick marks
Draw whiskers (horizontal lines) from the box to the extremes