Numerical errors usually occur for one of these five reasons:
- A journalist mishears a correct number given to them by a source and fails to double-check it.
- A source unwittingly provides a mistaken piece of information and the journalist fails to verify it.
- A source deliberately fudges the numbers and the journalist fails to verify them.
- A journalist or editor miscalculates a figure.
- A journalist re-reports a mistake made by another media outlet.