What is the IQR formula?

The Interquartile Range Formula appears as "Q3 - Q1," where Q3 is the upper quartile and Q1 is the lower quartile of a data set. The interquartile range is also commonly referred to as the middle fifty or midspread.

The range is a measure of spread and may be used to determine whether data have a normal distribution and in locating outliers in a data set. Significant differences in standard deviation and z-score indicate an abnormally distributed population, while extremely low and extremely high values beyond the whiskers of a box plot used to show distribution are known as outliers.