Drivers for ride-hailing services Uber and Lyft, as well as other workers in the so-called "gig economy," are earning less than they were five years ago, according to a new study. But Uber and Lyft disputed the findings, claiming researchers' methodology was flawed.

On average, drivers who transported people (Uber and Lyft) and packages (Uber Eats and Postmates) working through apps earned 53 percent less in 2017 than they did in 2013, according to a JPMorgan Chase Institute study. The study looked at online payments from gig-economy services into Chase checking accounts.

The average monthly payments to drivers working for transportation services declined during the period studied from $1,469 to $783. But the study found that people working for Airbnb, Turo, and Parklee—which let users rent their homes, cars, and parking spaces, respectively—saw monthly payments increase 69 percent, to an average $1,736.

The study also recorded an increase in the number of people working in transportation-related jobs within the gig economy. The total share of the working population involved in the gig economy at any point in a year increased from 2 percent in 2013 to nearly 5 percent in 2018. Approximately half, or 2.4 percent, have worked in transportation jobs so far this year. This number is up by a small fraction of the total in 2013.

JPMorgan Chase supplied a number of possible reasons for the decrease in earnings, which include drivers working fewer hours, a decrease in trip prices, and Uber and Lyft paying drivers lower rates. Researchers also noted that demand for ride-hailing services may not have increased to match the larger number of drivers.

In a blog post responding to the study, Uber attributed the findings to growth in drivers who choose to work part-time.

"The study's findings reinforce what we and many other have been saying for some time: that the number of people involved in flexible work arrangements is growing, and that growth is driven, in large part, by people who use platforms like Uber on the side." Uber has long maintained that most of its drivers are part-timers who aren't interested in working full time, or are using ride hailing to supplement income from an existing job. The company claims that more than 50 percent of its U.S. drivers work less than 10 hours per week.

Uber also took issue with JPMorgan Chase's use of monthly earnings as the metric for the study. An increased number of drivers would naturally lead to a decrease in each driver's monthly earnings, Uber said. The company said hourly earnings would be a "more appropriate metric," and claimed its own previous research showed that these earnings "have remained stable over time." Uber's biggest U.S. competitor, Lyft, offered similar sentiments.

"The fact that this study did not examine hourly earnings, the metric that drivers care most about, has resulted in misleading headlines. Had it done so, the results would have shown stable driver earnings in recent years. Many more drivers are choosing to earn with Lyft on a part-time basis, often fewer than ten hours per week, and they tell us they truly value the flexibility Lyft provides," Lyft spokesperson Adrian Durbin said in a statement. He added that Lyft agrees with the analysis published by Uber in its blog post.

For the study, JPMorgan Chase focused on jobs mediated through online platforms, but other studies of the gig economy have included freelance or contract work as well, noted Recode. The study covered activity in 39 million Chase checking accounts between 2012 and 2018. During the period studied, the number of apps involved rose from 42 to 128. Researchers had the advantage of looking at objective data, rather than subjective survey responses. However, even with 128 apps, it may not have been an all-inclusive study. It also doesn't account for transactions through services such as PayPal, and is subject to the demographic peculiarities of Chase account holders.