Benford’s law (single and double digits)
First Digit Law: Percentage of time digits 1 through 9 are expected to occur in the first position in a genuine data set of numbers.
First Two Digits Law: Percentage of time digits 10 through 99 are expected to occur in the first two positions in a genuine data set of numbers.
How to use it ?
If an employee is committing fraud by producing fraudulent invoices, the amounts are not generated radomly, employee has to create a ficticious amount. These amounts can become outliers in Benford's law affecting expected frequencies for each first/first-Two digit(s) of the invoice amount.