The import statistics are initially collected and compiled in terms of approximately 18,000 10-digit commodity codes in the HTSA. The HTSA is maintained by the U.S. International Trade Commission and is based on the 2-, 4-, and 6-digit headings and subheadings of the international Harmonized System (HS). The HTSA is revised and published at least twice annually; new codes are usually effective January 1 and July 1. Suggested changes to the statistical requirements of the HTSA should be submitted in the form of a request to the 484(f) Committee. For more information, see http://hts.usitc.gov/.