The percentage of US workers engaged in “alternative work arrangements” mushroomed to 15.8% in late 2015 from 10.1% in February 2005, according to new research from Lawrence Katz of Harvard University and Alan Krueger of Princeton University.

“A striking implication of these estimates is that all of the net employment growth in the US economy from 2005 to 2015 appears to have occurred in alternative work arrangements,” according to the study.

It also mentioned the increase in alternative work arrangements is particularly noteworthy since the percent of worker in such jobs was little changed from 1995 to 2005, according to the US Bureau of Labor Statistics research.

Still, relatively few worked through online platforms such as Uber or TaskRabbit in 2015. Only 0.5% of all US workers did, the study said.

It defined alternative work arrangements as temporary help agency workers, on-call workers, contract company workers (individuals who worked for a company that contract out their services), and independent contractors or freelancers.

The study aimed to measure the contingent workforce in the same vein as the US Bureau of Labor Statistics, which last measured the contingent workforce in 2005. Katz’s and Krueger’s survey included completed questionnaires from 3,844 people.

Katz’s and Krueger’s study, “The Rise and Nature of Alternative Work Arrangements in the United States, 1995-2015” is available online.

Other studies with separate methodologies point to increases in the contingent workforce. One study by MBO Partners last year found that the number of full-time and part-time independent workers in the US rose 12% since 2011 but held steady between 2015 and 2014.