Groupon Shares Backpedal

Shares of Groupon Inc. tumbled 15% Tuesday to end near the $20-a-share price of the daily-deals company's recent $805 million initial public offering.

Analysts attributed the stock's biggest one-day loss since its Nov. 3 IPO to concerns about the health of the e-commerce market and rising competition, as well as factors that may have helped short-sellers, who have taken an interest in the company.