Outlier

An outlier is a value far away from the others. It can be a typo, a measurement error - or a real, unusual answer.

Example: No. 76 has 9 points, everyone else 26 to 88. Without this value, the difference between the groups would be 8.0 instead of 6.8 points.

Caution: Never delete outliers silently. Check the original first. If a value is left out, say so in the report and give the reason.