and use the sale proceeds to prepay the mortgage as part of a physical relocation. In addition, changes to the GSE's underwriting standards, further modifications to existing U.S. Government sponsored programs such as HARP, or the implementation of new programs can have a significant impact on the rate of prepayments. Further, GSE buyouts of loans in imminent risk of default, loans that have been modified, or loans that have defaulted will generally be reflected as prepayments on agency securities and also increase the uncertainty around our estimates. Consequently, under different conditions, we could report materially different amounts. Item 7A. Quantitative and Qualitative Disclosures About Market Risk in this Annual Report on Form 10-K includes the estimated change in our net interest income should interest rates go up or down by 50 and 100 basis points, assuming the yield curves of the rate shocks will be parallel to each other and the current yield curve.
Fair Value of Investment Securities
We estimate the fair value of our agency securities based on a market approach using "Level 2" inputs from third-party pricing services and non-binding dealer quotes derived from common market pricing methods. Such methods incorporate, but are not limited to, reported trades and executable bid and ask prices for similar securities, benchmark interest rate curves, such as the spread to the U.S. Treasury rate and interest rate swap curves, convexity, duration and the underlying characteristics of the particular security, including coupon, periodic and life caps, rate reset period, issuer, additional credit support and expected life of the security. We generally obtain 3 to 6 quotes or prices (referred to as "marks") per agency security. We attempt to validate marks obtained from pricing services and broker dealers by comparing them to our recent completed transactions involving the same or similar securities on or near the reporting date. Changes in the market environment and other events that may occur over the life of our investments may cause the gains or losses ultimately realized on these investments to be different than the valuations currently estimated.
We also evaluate our agency securities for other-than-temporary impairment ("OTTI") on at least a quarterly basis. The determination of whether a security is other-than-temporarily impaired may involve judgments and assumptions based on subjective and objective factors. When a security is impaired, an OTTI is considered to have occurred if any one of the following three conditions exist as of the financial reporting date: (i) we intend to sell the security (that is, a decision has been made to sell the security), (ii) it is more likely than not that we will be required to sell the security before recovery of its amortized cost basis or (iii) we do not expect to recover the security's amortized cost basis, even if we do not intend to sell the security and it is not more likely than not that we will be required to sell the security. A general allowance for unidentified impairments in a portfolio of securities is not permitted.
If either of the first two conditions exists as of the financial reporting date, the entire amount of the impairment loss, if any, is recognized in earnings as a realized loss and the cost basis of the security is adjusted to its fair value. If the third condition exists, the OTTI is separated into (i) the amount relating to credit loss (the "credit component") and (ii) the amount relating to all other factors (the "non-credit components"). Only the credit component is recognized in earnings, with the non-credit components recognized in OCI. However, in evaluating if the third condition exists, our investments in agency securities typically would not have a credit component since the principal and interest are guaranteed by a GSE and, therefore, any unrealized loss is not the result of a credit loss. In addition, since we designate our agency securities as available-for-sale securities with unrealized gains and losses already recognized in OCI, any impairment loss for non-credit components is already recognized in OCI.
The liquidity of the agency securities market allows us to obtain competitive bids and execute on a sale transaction typically within a day of making the decision to sell a security and, therefore, we generally do not make decisions to sell specific agency securities until shortly prior to initiating a sell order. In some instances, we may sell specific agency securities by delivering such securities into existing short to-be-announced ("TBA") contracts. TBA market conventions require the identification of the specific securities to be delivered no later than 48 hours prior to settlement. If we settle a short TBA contract through the delivery of securities, we will generally identify the specific securities to be delivered within one to two days of the 48-hour deadline.
Derivative Financial Instruments/Hedging Activity
We maintain a risk management strategy, under which we may use a variety of derivative instruments to economically
hedge some of our exposure to market risks, including interest rate risk, prepayment risk and extension risk. Our risk management objective is to reduce fluctuations in net book value over a range of interest rate scenarios. The principal instruments that we use are interest rate swaps and options to enter into interest rate swaps ("interest rate swaptions"). We also utilize forward contracts for the purchase or sale of agency MBS securities on a generic pool, or a TBA contract, basis and on a non-generic, specified pool basis, and we utilize U.S. Treasury securities and U.S. Treasury futures contracts, primarily through short sales. We may also purchase or write put or call options on TBA securities and we may invest in other types of mortgage derivatives, such as interest-only securities, and synthetic total return swaps, such as the Markit IOS Synthetic Total Return Swap Index ("Markit IOS Index").