To address inflation risk, the U.S. treasury introduced a new type of bond in 1997 - the Treasury inflation-indexed security. The interest rate paid by the bond will remain constant during the life of the bond, but the principal will be adjusted semiannually to reflect inflation. In periods of rising prices, the principal of a Treasury inflation-indexed security will increase. This means that the interest payments will also rise because they are based on a larger principal amount. As a result, the buying power of the interest payments and the principal should remain steady even during periods of rapid inflation. Of course, prices don't always rise. In a period of deflation (in other words, a time of falling prices), the principal amount of a Treasury inflation-indexed security might be reduced. However, when the principal amount is repaid at maturity, the investor will receive the larger of the inflation-adjusted principal or the face amount even if deflation had reduced the adjusted principal amount to a sum that is less than the security's face amount. If this new type of bond is well received by investors, the U.S. Treasury plans to offer them in a variety of maturities. Today, there are a few mutual funds that specialize in these inflation-indexed bonds. Many funds are actively managed, meaning that the investment adviser uses economic, financial, and market analyses when deciding which bonds to buy or sell. Manager risk refers to the possibility that the investment adviser may fail to choose an effective investment strategy or to execute that strategy well. As a result, an investor in the fund may lose money. Some managers limit their investments to issues rated Baa or higher by Moody's Investors. Despite the relatively low credit risk of investment-grade corporate bond funds, they do not match the quality level of U.S. government bond funds. As a result, corporate bond funds generally pay higher yields than U.S. government bond funds. Some bond funds also may be exposed to event risk, the possibility that some corporate bonds may suffer a substantial decline in credit quality and market value because of a corporate restructuring for example, a merger, leveraged buyout, or takeover. Restructurings are sometimes financed by a significant increase in the company's debt an added burden that could hurt the credit quality of the company's existing bonds. Still more risks can arise from the use of derivatives, such as futures or options, whose values are linked to (or derived from) the value of another asset or commodity. Because different derivative-trading strategies carry different amounts of potential risk and reward, some funds limit the use of derivatives by their portfolio managers.