The review article is titled,”Self-Employment in the United States” and was published as a “Spotlight on Statistics” by the U.S. Bureau of Labor Statistics (BLS).
From the Intro:
Since the late 1940s, data on self-employment have been collected regularly as part of the Current Population Survey (CPS), a monthly sample survey of about 60,000 households that provides employment and unemployment data for the nation’s civilian noninstitutional population ages 16 and older. Since 1967, the official BLS estimates of self-employment have included only the unincorporated self-employed.
Although it is possible to identify the incorporated self-employed separately, they are counted as wage and salary workers in the official statistics because, legally, they are employees of their own business. This Spotlight on Statistics examines recent trends in self-employment by various demographic and socioeconomic characteristics, including both the unincorporated and the incorporated self-employed, as well as data on paid employees who work for the self-employed.