outlier

In statistics, an outlier is a data point that is significantly different from other observations in a dataset. These values can appear unusually large or small compared to the rest of the data.12

Outliers can sometimes result from errors in data collection or entry. Experienced statisticians carefully review outliers to determine if they are accurate and appropriate for inclusion in the dataset. If an error is found, the data value may be corrected or removed.1

Statistical measures like the mean and standard deviation are used to identify outliers. A common method involves calculating a z-score for each data value, which indicates how many standard deviations it is from the mean. Values with a z-score below -3 or above +3 are often considered outliers.1