Outliers are considered anomalities in a data set but are still represented in graphical data such as in box plots.

To calculate whether a data point is considered a possible outlier or not, it must be further than 1.5 times the IQR away from the ends of the first quartile and third quartile for it to be an outlier.

The general process for determining outliers is then given by:

  1. First calculate the IQR, which is given by IQR = Q_3 - Q_1
  2. Then find the range of values which would be considered outliers. Lower outlier values will have to be less than Q_1 - 1.5 \times IQR and high outlier values will have to be greater than Q_3 + 1.5 \times IQR .
  3. If there are any values outside these values, then it is considered an outlier.

See also: