Box and whiskers plotBefore studying this lesson, you need to understand the median. Basically a box and whiskers plot looks like this: Just like the name suggests, the rectangle you see is called a box. And the reason we call the two lines extending from the edge of the box whiskers is simply because they look like whiskers or mustache, especially mustache of a cat The five points or dot that you see represents the followings starting from left to right Lower extreme: the lowest or smallest value in a set of data Lower quartile or first quartile: the median of all data below the median Median or second quartile: the middle value of the set of data. If there are two values in the middle, the median is the average of the two values Upper quartile or third quartile: the median of all data above the median Upper extreme: The biggest value in the set Example: Construct a box and whiskers plot for the data set: {5, 2, 16, 9, 13, 7, 10} First, you have to put the data set in order from greatest to least or from least to greatest From least to greatest we get : 2 5 7 9 10 13 16 Since the smallest value in the set is 2, the lower extreme is 2 Since the greatest value in the set is 16, the upper extreme is 16 Now, look carefully at the set: 2 5 7 9 10 13 16 You can see that 9 is located right in the middle of the set of data Therefore, 9 is the median Now to get the lower quartile, you need all data before the median or 9 2 5 7 9 10 13 16 In bold right above we show all data before 9, so 2 5 7 Since the value in the middle for the set 2 5 7 is 5, the lower quartile is 5 Finally, to get the upper quartile, you need all data after the median or 9 2 5 7 9 10 13 16 In bold right above we show all data after 9, so 10 13 16 Since the value in the middle for the set 10 13 16 is 13, the upper quartile is 13 Now make a number line and graph above the number line 2, 5, 9, 13, and 16 with five dots: one dot will represent the median, one dot will represent each extreme, finally, one dot will represent each quartile. Your graph should look like this after you are done Draw a rectangle or box starting from the lower quartile to the upper quartile. Draw a vertical segment too to represent the median Finally, draw horizontal segments or whiskers that connect all five dots together. The box and whiskers plot for {5, 2, 16, 9, 13, 7, 10} is : 




 HomepageMeasures of central tendency
Finding the mode
Finding the median
Box and whiskers plot
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