Groupon Inc. GRPN +3.84% said it was revising lower the financial results it reported for its fourth quarter, after discovering the company had to set aside more money for customer refunds. The online-coupon site, which went public in November, said its auditor, Ernst & Young, discovered a "material weakness in its internal controls" for the fiscal year. The accounting changes will reduce the Chicago company's revenue for the period by $14.3 million and reduce net income by $22.6 million, or 4 cents a share.