The IRS feeds all returns into a computer, which assigns them a score based on a scientifically measured system known as DiscriminantFunction “DIF.” Your return is compared with a complicated set of standards, arrived at partially by deductions claimed by others in your income bracket. An average profile is established and if your return varies drastically, it is flagged by the computer. The higher the DIF score, the higher the potential for audit.

IRS Website: http://www.irs.gov/

From: How Do They Do That? By: Caroline Sutton