About 250,000 Americans earn more than 75% of their income from online labor platforms
This is a preliminary calculation. Please let me know if I appear to have made a mistake.
Diana Farrell and Fiona Greig, in their 2016 report Paychecks, Paydays, and the Online Platform Economy (JP Morgan Chase Institute), write that 0.4% of adults “actively participate in” (receive income from) labor platforms each month (p. 21), and “labor platform income represented more than 75 percent of total income for 25 percent of active participants” (p. 24).
“Labor platforms” here include both platforms for in-person work such as Uber as well as platforms for remote work such as Amazon Mechanical Turk and Upwork.
Per the CIA World Factbook, the US total population is 321,369,000, with approximately 80.1% “adult” (“15 years or older”).
Therefore the number of US adults earning more than 75% of their income from labor platforms is approximately 0.25 * 0.004 * 0.801 * 321369000, or 257,415.
“Adults” is interpreted by Farrell and Greig as “18 years or older,” not “15 years or older,” so I round down to 250,000.