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A box-and-whisker plot is a graph of the following five statistics (5 number summaries). It is used to investigate population characteristics when there are outliers in the data or when the distribution of the population is unknown.
[Figure1]
How to draw a box-and-whisker plot
The table shows various statistics based on the results of a questionnaire that investigated the number of meetings held per month by employees working for a company. Let’s draw a box-and-whisker plot by age based on the table.
[Table] Box-and-whisker plot statistics table
How to draw a box-and-whisker plot
1) Check the maximum value, minimum value, first quartile, median, and third quartile of the data
2) Draw a rectangle bounded by the first and third quartiles
3) Draw dividers to divide that rectangle at the median
As shown below, the distribution and characteristics by age can be clearly understood by drawing a box-and-whisker plot.
[Figure2]
Notes on box-and-whisker plot
The advantage of the box-and-whisker plot method over other statistical analysis methods, is that it becomes relatively easier to grasp the variation in the data. In addition, by drawing each group of data, as described above, we can check the variation in each data point.
Thus, box-and-whisker plots can easily visualize data variations and are used as a method for checking data distribution.
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