Gig work is sweeping advanced economies, but workers on digital platforms like Airbnb and Uber make up just a small share of the independent labor force.

About 27 percent of America’s working-age population engages in independent work, according to a McKinsey Global Institute survey, and the share is even larger in France and Spain. While only about 4 percent of the working-age population in the U.S. and Europe use online gig-work marketplaces, “rapid growth of the largest platforms suggests we have only just begun to see their impact.”

Even as studies and anecdotes suggest that a growing number of people use short-term jobs as a primary or secondary source of income, data on the actual size of the gig workforce have thus far been limited. Understanding the scope of independent work could be important for fiscal and monetary policymakers as they try to comprehend trends like the rise in part-time employment and the declining jobless rate.

“When we talk about the unemployment rate, we’re focusing on the idea that everyone has one job,” said Susan Lund, one of the report’s authors. “For policy makers and for companies, I think there’s been this mythology around what is a job, what is work.”

The authors defined independent work as having autonomy, payment by task or assignment, and a short-term relationship with the client, and supplemented existing government data with a six-country survey to arrive at their results. Here are three charts that detail what they found:

• The share of workers taking on these jobs is largest in Spain as a share of the population, followed by France. The U.S. is in the middle of the pack.

• In the U.S., young people are the most likely to be independent workers, and in Spain, low-income households are also very likely to do short-term jobs.

• In the U.S. and Germany, a large share of independent workers are casual earners or free agents who actively choose the lifestyle. In France and Spain, workers often pick up jobs out of necessity.So what’s next for this workforce? The tiny portion of workers who are using platforms like Uber, Etsy and TaskRabbit to get jobs has room to grow, the authors said.

“As digital platforms expand, they could have a transformative effect when applied to the labor market,” they write. “Digital technologies have made it possible for new players to enter ecosystems of independent work and provide better matching mechanisms, in some cases creating new demand and making new types of independent earning activities possible.”