A pair of columns are functionally dependent if the values in one column can reliably predict the values in another column. For example, if a dataset contains an Employer ID column and a date of birth column, the date of birth should be the same in all rows that contain a given Employer ID.

Functional dependencies can highlight potential data quality issues by identifying records the records that do not conform to a column functional dependency. For example, if 99.8% of rows in a data source are functionally dependent, there is a high likelihood that the remaining rows may contain incorrect information.