Stocks fell significantly on Thursday as investors worried about the global economic recovery following mixed U.S. economic data and a key ratings downgrade. It was the major indexes' third consecutive decline. Standard & Poor's affirmed Britain's top-tier credit rating but lowered its outlook for the country to “negative' from “stable.” S&P said its revision was based on the possibility that Britain's debt burden could reach 100 percent of its gross domestic product, despite the British government's “further fiscal tightening.” The news raised concerns that other major economies that have borrowed heavily to fund economic stimulus efforts, including the United States, could face similar downgrades. In economic news, U.S. jobless claims declined slightly last week, while the number of Americans continuing to receive unemployment assistance grew to 6.6 million, a record high, the government reported. A private research organization said its index of leading economic indicators—which predicts U.S. economic activity in the coming three to six months—rose 1 percent in April, the first gain in seven months, suggesting the recession may be nearing an end. Light sweet crude oil for July delivery fell from its six-month high, losing 99 cents to close at $61.05 a barrel on the New York Mercantile Exchange. The U.S. dollar rose versus the euro, the yen, and the British pound. The Dow Jones industrial average fell 129.91, or 1.5 percent, to 8,292.13. The broader S&P 500 fell 15.14, or 1.7 percent, to 888.33. The technology-heavy Nasdaq composite index fell 32.59, or 1.9 percent, to 1,695.25. In one of the first initial public offerings of the year, OpenTable, which operates a restaurant reservation system, raised $60 million, Reuters reported. The company priced its shares at $20 each, which was higher than expected, and they rose 59 percent to $31.89. The New York Stock Exchange composite index fell 89.85 to 5,780.54. The American Stock Exchange composite index fell 10.63 to 1,522.67. And the Russell 2000 index fell 8.13 to 481.22.