The box plots discussed in this section are often called skeletal (or regular) box plots. Modified box plots are constructed as follows:
a. Calculate the difference between the quartiles Q3 and Q, and denote it as IQR (interquartile range), so that IQR = Q3 - Q,.
b. Draw the box with the median and quartiles as usual, but when extending the lines that branch out from the box, go only as far as the scores that are within 1.5 IQR of the box.
c. Mild outliers are scores above Q3 by an amount of 1.5 IQR to 3 IQR, or below Q, by an amount of 1.5 IQR to 3 IQR. Plot mild outliers as solid dots.
d. Extreme outliers are scores that exceed Q3 by more than 3 IQR or are below Q( by an amount more than 3 IQR. Plot extreme outliers as small hollow circles.
The accompanying figure is an example of the box plot described here. Use this procedure to construct the box plot for the given scores, and identify any mild outliers or extreme outliers.
3 15 17 18 21 21 22 25 27 30 38 49 68

Mild Extreme Outliers Outliers Median l Mild Outlier 3IQR