According to the IRS website, a number of distinct factors can trigger a review, including the need to verify the following entries on your return:
Income is not overstated or understated.
Tax withholding amounts are correct [especially if your employer failed to remit them to the IRS].
You have the right to claim the tax credits on your return.
Social Security benefits withholding amounts are correct.
Household help is accurately reported.
Schedule C income is not overstated or understated.
Or your return may have been selected at random for a review.
