"Bans on short-selling imposed during the financial crisis in the belief that short sales were driving United States stock prices below fundamental values did little to stabilize those prices, according to a new study by New York Fed economists. In addition, the bans had the unwanted effects of lowering market liquidity and boosting trading costs. In Market Declines: What Is Accomplished by Banning Short-Selling? New York Fed economist Hamid Mehran and Notre Dame finance professors Robert Battalio and Paul Schultz investigate the link between short-selling and market downturns. The authors first evaluate evidence on the bans’ effectiveness in limiting share price declines in 2008. To provide additional evidence, the three then consider the market effects of short-selling in August 2011, when the debt-rating agency Standard and Poor’s lowered the U.S. sovereign long-term credit rating, prompting the S&P 500 to fall 6.66 percent on the next trading day. At the time, there was no short-selling ban in place in the U.S."