S&P's Most Shorted

Shares of Sears and AK Steel have seen a more than 50 percent jump in short-interest since early August. Both companies are down 12 and 20 percent, respectively, in the past two months.

According to the latest data on short interest, First Solar and Sears have the highest short-interest in the S&P 500 index, standing at more than 30 percent.

Short-interest measures the total number of shares of a security that have been sold short expressed as a percent of total tradable shares.

Investors track short interest levels to gain a sense of where a stock might be headed, along with some insight into whether any positive news might force short-traders to cover their positions, pushing stocks higher.

Express Scripts, Moody's and Pitney Bowes have joined the top 20 most shorted companies since early August. In comparison, Monster Worldwide, R.R. Donnelley & Sons and Washington Post have fallen off the list.

Below is a list of the most heavily shorted stocks along with the percent change in stock price and short interest in the past two months.

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