The rapidly growing technology company Uber released internal data Thursday arguing that drivers who use the app to give rides-for-hire in their personal cars are making more money as chauffeurs than professional taxi drivers do – as much as $17 an hour in Washington and Los Angeles, $23 in San Francisco and $30 in New York.

Those numbers, released as part of the most extensive peek yet into its business model, have only inflamed debate about what companies like Uber mean for the economy and whether the kind of work they offer is sustainable for the tens of thousands of people who’ve signed up.

Uber and its boosters say those earnings – and the breakneck pace at which drivers are joining its ranks – offer proof that the company is creating new kinds of opportunity for workers who want neither a 9-to-5 job nor a boss. But some of its drivers and the taxi industry counter that Uber’s earnings data leave out a critical piece of the equation: the steep costs people must pay to operate their own cars as modern-day taxis.

Uber released the new data in a report co-written by Princeton economist Alan Krueger, a former chairman of President Obama’s Council of Economic Advisors. The analysis, which includes a survey of 601 drivers, suggests that Uber’s drivers look notably different from your typical cabbie: Nearly half of the Uber drivers surveyed had at least a college degree, compared to 19 percent for taxi drivers and chauffeurs as reflected in government occupational data.

The analysis also reveals for the first time the size of Uber’s driver pool in the U.S. and the rate at which it’s rapidly expanding. In December, 162,037 “active drivers” completed at least four or more trips for the service. The number of new drivers signing up has doubled every six months for the past two years.

“The more I looked into it, the more I thought this rapid growth is really not a result of a weak job market, but the result of a new opportunity,” says Krueger, who was contracted by Uber to conduct the study.

As Uber has grown into a tech giant valued by investors at more than $40 billion, it has become something of an economic Rorschach test. Some see in it the hopeful future of work in a digital age, where anyone with a car (or a home, or a service to offer) can be his own boss, choosing hours and determining income with a flexibility that makes other pursuits more feasible.

Critics, meanwhile, see in Uber something more bleak, a sign that people who can’t find better jobs in a bad economy must settle instead for work as part-time “independent contractors” with a tech company that offers them no benefits. For these critics, the numbers Uber released Thursday did little to dispel that skepticism.

“This report is designed to impress American mayors and disguise the predatory nature of Uber’s relationship to its drivers – the company collects money, while the drivers accept all of the risk,” said Dave Sutton, spokesman from the Taxicab, Limousine & Paratransit Association.

Uber’s earnings data suggested that drivers in its biggest markets are making about $6 an hour more than local taxi drivers and chauffeurs. But Sutton said the comparison is unfair given that Uber drivers must deduct the costs of gas, car insurance and vehicle maintenance.