Although Improvements Have Been Made, More Can Be Done to Identify Businesses by Their Principal Business Activity, July 2006, Reference Number: 2006-30-097 (21 pages, PDF). “This report presents the results of our review of the Internal Revenue Service’s (IRS) efforts to identify businesses by their principal business activity. The overall objective of this review was to evaluate the effectiveness of the corrective actions taken in response to the recommendations in a prior Treasury Inspector General for Tax Administration report.”