LAS VEGAS, NEVADA — Journalists in Las Vegas tracked fluctuating prices on digital shopping platforms over a 14-day period, documenting variations in Old Navy online cart prices and Uber delivery fees for McDonald's orders.

Juliana Kaplan tracked price changes over 14 days for items she left in her digital Old Navy shopping cart. A group of journalists ordered the same item from the same McDonald's location at the same time using the Uber platform. Fees for the same McDonald's order via Uber varied by about 20 cents among customers.

Mark Tremblay, an assistant economics professor at the University of Nevada, Las Vegas who studies the digital economy, addressed questions about predicting price fluctuations. "If I knew that, I wouldn't be talking to you, and I'd be investing in stocks, right?" Tremblay said.