Box-and-Whisker Plots

Important Terms Median:The middle number in a set of data when the data are arranged in numerical order. Quartile:One of four equal parts of data from a large set of data. Upper Quartile:The median of the upper half of a set of numbers. Lower Quartile:The median of the lower half of a set of numbers. Lower Extreme:The least number in a set of data. Upper Extreme:The greatest number in a set of data. Outliers:Data that is more than 1.5 times the inner quartile range, from the quartiles.

Step 1 Put the data in order from the least to the greatest. Data: Automobile gas mileages Find the median - 24

Step 2 Find the median of the first half of the data This is called the Lower Quartile LQ -

Step 3 Find the median of the upper half of the data This is called the Upper Quartile UQ - Inter Quartile Range - the difference between the UQ and the LQ = 14IR = UQ - LQ

Step 4a Find the lowest number This is called the Lower Extreme LE - Find the highest number This is called the Upper Extreme 48UE - Step 4b

Step Draw and label a number line with your 5 points LEUEUQLQMedian

Step 5 continued Draw a box starting at the lower quartile and ending at the upper quartile Draw a vertical line through the median value.

Step 5 continued Draw a line from the lowest number to the lower quartile and one from the highest number to the upper quartile “The Whiskers”

A box - and - whisker plot divides data into four equal parts that represent 25% of the data % of the data falls between the LE and the LQ. 25% of the data falls between the LQ and the median. 25% of the data falls between the median and the UQ. 25% of the data falls between the UQ and the UE.

You Try It! Make a box-and-whisker plot for the following recent test scores

Note: Because there is an even number of data, you have to take the average of the two middle numbers to determine the median. Median - Lower Quartile - 74 Upper Quartile - 90 Lower Extreme - 62 Upper Extreme - 98

Recent Test Scores