Anomaly
Anything in a dataset that does not fit the expected pattern: an order dated before the customer signed up, or a day with far more rows than usual.
An outlier is one kind of anomaly, a single value far from the rest. Anomalies also include odd combinations and odd patterns, where each value looks fine by itself.
Where it comes up
- Outliers from entry errorsA value sits far outside the rest because of a slipped key, an extra zero, or a misplaced decimal point.
- Impossible datesA value is shaped like a date but names a day that does not exist or could not have happened.
See also
- OutlierA value far from the rest of its column. It may be an error, or it may be the most interesting row in the file.
- Data profilingExamining a dataset to describe what is actually in it: types, ranges, distinct values, blanks, and patterns, column by column.
- ValidationChecking values against rules, such as a date being in the past or a state code being on the allowed list, and reporting what fails.