For further information, please refer to the US Census Bureau's Annual Services release, online at http://www.census.gov/services/.
Source: US. Bureau of the Census
Release: Annual Services Survey
US. Bureau of the Census, Sources of Revenue: Bookkeeping, Compilation, Billing, and Collection Services for Accounting, Tax Preparation, Bookkeeping, and Payroll Services, All Establishments, Employer Firms [REVBCCEF5412ALLEST], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/REVBCCEF5412ALLEST/, September 5, 2015.