Find the quartiles and interquartile range (IQR) of a data set. Enter the numbers separated by commas.
Usage Tip
Unlike range, the IQR ignores extreme values — it is the basis of the box in a box-and-whisker plot.
IQR = Q3 − Q1
The interquartile range is the spread of the middle half, a measure of variability resistant to outliers.
Q1 and Q3 are the medians of the lower and upper halves.
The IQR is used to detect outliers (beyond 1.5 times IQR past a quartile).
Quartiles split sorted data into four parts. The first quartile marks the value below which about a quarter of the data falls, the second is the median, and the third marks the point below which about three quarters falls. The interquartile range is the third quartile minus the first, and it measures the spread of the middle half of the data.
Because the interquartile range ignores the extremes, it is less affected by outliers than the full range. A common rule flags values more than one and a half times the interquartile range beyond the quartiles as possible outliers. Different textbooks and software use slightly different methods for finding quartiles, so results can vary by a small amount on small data sets.