Our geometry test example did not have any outliers, even though the score of 53 seemed much smaller than the rest, it wasn't small enough. These are represented by a dot at either end of the plot. Outliers are values that are much bigger or smaller than the rest of the data. If you scored somewhere in the lower whisker, you may want to find a little more time to study. If your score was in the upper whisker, you could feel pretty proud that you scored better than 75% of your classmates. Using this plot we can see that 50% of the students scored between 69 and 87 points, 75% of the students scored lower than 87 points, and 50% scored above 79. Since there is an equal amount of data in each group, each of those sections represents 25% of the data. This plot is broken into four different groups: the lower whisker, the lower half of the box, the upper half of the box, and the upper whisker. Draw a box from Q1 to Q3 with a line dividing the box at Q2. Then extend "whiskers" from each end of the box to the extreme values. It should stretch a little beyond each extreme value. Create a number line that will contain all of the data values. Find the extreme values: these are the largest and smallest data values. Find the median of the data greater than Q2. Step 3: Find the median of the data less than Q2.
Step 1: Order the data from least to greatest. Let's start by making a box-and-whisker plot (also known as a "box plot") of the geometry test scores we saw earlier:ĩ0, 94, 53, 68, 79, 84, 87, 72, 70, 69, 65, 89, 85, 83, 72 Extreme Values – the smallest and largest values in a data set.IQR – interquartile range, the difference from Q3 to Q1.Q3 – quartile 3, the median of the upper half of the data set.Q2 – quartile 2, the median of the entire data set.Q1 – quartile 1, the median of the lower half of the data set.There are a few important vocabulary terms to know in order to graph a box-and-whisker plot. It's a nice plot to use when analyzing how your data is skewed. The box-and-whisker plot doesn't show frequency, and it doesn't display each individual statistic, but it clearly shows where the middle of the data lies. Box-and-whisker plots are a handy way to display data broken into four quartiles, each with an equal number of data values.
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