Outlier Calculator

An outlier in a distribution is a number that is more than 1.5 times the length of the box away from either the lower or upper quartiles. Specifically, if a number is less than Q1 – 1.5×IQR or greater than Q3 + 1.5×IQR, then it is an outlier.

In descriptive statistics, the interquartile range (IQR) is a measure of statistical dispersion, being equal to the difference between the third quartile (Q3) and first quartile (Q1), that is, IQR = Q3 – Q1.

The first quartile, also called the lower quartile, is equal to the data at the 25th percentile of the data. The third quartile, also called the upper quartile, is equal to the data at the 75th percentile of the data.

There are several different methods for calculating quartiles. This calculator uses a method described by Moore and McCabe to find quartile values. The same method is also used by the TI-83 to calculate quartile values. With this method, the first quartile is the median of the numbers below the median, and the third quartile is the median of the numbers above the median.