Self-employment income at low earnings levels.

If self-employment were much more prevalent at moderate and high earnings levels than at low levels and if the incidence of both the employee and employer taxes on wages is on the employee, then the social security tax structure would be regressive relative to taxable earnings. Analysis shows, however, that this is the case only in a very limited sense. For 1970, 6.5 percent of taxable earnings derives from self-employment. At least 6.3 percent of taxable earnings consists of self-employment income in each observed interval from $400 to $3,600. The proportion declines slightly with rising earnings until near the taxable maximum, when it begins to rise. If the average tax rate on earnings up to the maximum were tabulated by earnings both below and above the maximum, it appears very likely that mild regressivity would be shown beyond the taxable maximum, but of not more than a few tenths of a percent.