http://en.wikipedia.org/wiki/Mark_to_market Financial Accounting Standards Board (FASB) Statement No. 157 “Fair Value Measurements”,<2> established some new rules related to valuation of assets and liabilities:
FAS Statement 157 includes the following:
A new definition of fair value;
A fair value hierarchy used to classify the source of information used in fair value measurements (i.e. market based or non-market based);
New disclosures of assets and liabilities measured at fair value; and
A modification of the long-standing accounting presumption that a measurement date-specific transaction price of an asset or liability equals its same measurement date-specific fair value.
FAS 157 defines "fair value" as: “The price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.”
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Although FAS 157 does not require fair value to be used on any new classes of assets, it does apply to assets and liabilities that are carried at fair value in accordance with other applicable rules. The accounting rules for which assets and liabilities are held at fair value are complex. Mutual funds and securities firms have carried their assets and some liabilities at fair value for decades in accordance with securities regulations and other accounting guidance. For commercial banks and other types of financial services firms, some asset classes are required to be carried at fair value, such as derivatives and marketable equity securities. For other types of assets, such as loan receivables and debt securities, it depends on whether the assets are held for trading (active buying and selling) or for investment. All trading assets are carried at fair value. Loans and debt securities that are held for investment or to maturity are carried at amortized cost, unless they are deemed to be impaired (in which case, a loss is recognized). However, if they are available for sale or held for sale, they are required to be carried at fair value or the lower of cost or fair value, respectively. (FAS 65 and FAS 114 cover the accounting for loans, and FAS 115 covers the accounting for securities.) Notwithstanding the above, companies are permitted to account for almost any financial instrument at fair value, which they might elect to do in lieu of hedge accounting (see FAS 159, "The Fair Value Option").
So banks have been valuing their Mortgage Backed Securities at their Fair Market value - periodically updated to the most current market conditions. but as the housing market began to deteriorate defaults started increasing and house prices stopped going upward and started drifting downward.
Former FDIC Chair William Isaac placed much of the blame for the subprime mortgage crisis on the Securities and Exchange Commission and its fair-value accounting rules, especially the requirement for banks to "mark-to-market" their assets, particularly the mortgage backed securities.<6>
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Because the market for these assets is distressed, it is difficult to sell many MBS at other than fire-sale prices, which may be below the actual value that the mortgage cash flow related to the MBS would merit. As initially interpreted by companies and their auditors, the typically lower sale value was used as the market value rather than the cash flow value. Many large financial institutions recognized significant losses during 2007 and 2008 as a result of marking-down MBS asset prices to market value.
The write down of these assets is what has put so many banks in weak balance sheet positions.