How can we measure the size of the new uber-driver-type economy?
Those are important and difficult questions to answer. Regarding Uber, Jonathan Hall (Uber) and Alan Krueger (Princeton) wrote a joint paper on An Analysis of the Labor Market for Uber's Driver-Partners in the United States. The paper provides the first comprehensive analysis of Uber's driver-partners, based on both survey data and anonymized, aggregated administrative data. The following figure documents the exponential growth in the number of active Uber driver-partners in the United States from mid-2012, when uberX was launched, to late 2014.


Source: Hall and Krueger (2015)

More generally, they point out that the Bureau of Labor Statistics (BLS) publishes a supplemental module to collect information on various forms of contingent and alternative work arrangements in the Current Population Survey (CPS) in 1995, 2001, and 2005 that provides the most informative data available, although it is now somewhat out of date. The BLS contingent worker supplement also measured the share of workers in alternative work arrangements, including independent contractors. Workers in the sharing economy can work part-time or full-time, or participate on a temporary or permanent basis, but they are almost universally working as independent contractors while they are participating in the sharing economy. Thus, evidence on independent contractors can provide relevant background for understanding the nature of the labor market in a sector that overlaps with the sharing economy.