How do i do a box and whisker plots?

Answer 1

To start, you need to identify the median of your set of data. After you have the median, split the remaining data into 2 groups, one with everything smaller than the median, one with everything larger. You then take the median of the 2 groups you just found in the previous step, the smaller one is called the first quartile and the larger one is called the 3rd quartile. Next, you have to find the smallest and largest numbers in the entire original set of data. Now, you should have 5 numbers, the minimum, 1st quartile, median, 3rd quartile, and maximum. To make our actual plot, you plot a scale along one axis and make a tick mark for each of the 5 values we found before. Then, create a line connection the minimum to the 1st quartile and the 3rd quartile to the maximum. Finally, connect the 1st quartile to the 3rd quartile with a rectangle and you're done!

In addition, some plots add one more feature to make it easier to spot outliers. What they do is start by finding the difference between the 1st and 3rd quartile which is called the IQR (Inter-Quartile Range). Then, you see if every number less than the 1st quartile (and larger than the 3rd) is more than 1.5 times the IQR away. If it is, you remove the line going through any such values and place a little box at the point. Any place that gets a box can be called an outlier.