Prior to conducting a test audit, the Department will set forth in writing a test audit plan and provide the taxpayer with an opportunity to review and comment on the plan. The plan will describe the time period subject to audit, the records subject to review, methods for selecting records, statistical estimation procedures including the taxpayer's right to request an increase in sample size and the manner in which any tax liability will be calculated based upon the records reviewed.
61 Pa. Code § 8a.8