Critical accounting policies

Fair value of financial instruments

Financial assets and financial liabilities in our trading portfolio, financial assets and liabilities designated at fair value and derivative instruments are recorded at fair value on the balance sheet, with changes in fair value recorded in net trading income in the income statement. Key judgments affecting this accounting policy relate to how we determine fair value for such assets and liabilities.

Where no active market exists, or where quoted prices are not otherwise available, we determine fair value using valuation techniques. In these cases, fair values are estimated from observable data in respect of similar financial instruments, using models to estimate the present value of expected future cash flows or other valuation techniques, using inputs existing at the balance sheet dates. If available, market observable inputs are applied to valuation models (level 2). In cases where market observable inputs are not available for all significant valuation parameters, they are estimated based on appropriate assumptions (level 3).

Valuation models are used primarily to value derivatives transacted in the over-the-counter market, including credit derivatives and unlisted securities with embedded derivatives. All valuation models are validated before they are used as a basis for financial reporting, and periodically reviewed thereafter, by qualified personnel independent of the area that created the model. Wherever possible, we compare valuations derived from models with prices of similar financial instruments, and with actual values when realized, in order to further validate and calibrate our models.

A variety of factors are incorporated into our models, including actual or estimated market prices and rates, such as time value and volatility and market depth and liquidity. Where available, we use market observable prices and rates derived from market verifiable data. Where such factors are not market observable, changes in assumptions could affect the reported fair value of financial instruments. We apply our models consistently from one period to the next, ensuring comparability and continuity of valuations over time, but estimating fair value inherently involves a significant degree of judgment. Management therefore establishes valuation adjustments to cover the risks associated with the estimation of unobservable input parameters and the assumptions within the models themselves. Valuation adjustments are also made to reflect such elements as deteriorating creditworthiness (including country-specific risks), concentrations in specific types of instruments and market risk factors (interest rates, currencies, etc.), and market depth and liquidity. Although a significant degree of judgment is, in some cases, required in establishing fair values, management believes that the fair values recorded in the balance sheet and the changes in fair values recorded in the income statement are reflective of the underlying economics, based on our established fair value and model governance policies and the related controls and procedural safeguards we employ. For a description of the valuations of our positions related to the US residential mortgage market see Note 26a).

Uncertainties associated with the use of model-based valuations (both level 2 and level 3) are predominantly addressed through the use of model reserves. These reserves reflect the amounts that UBS estimates are appropriate to deduct from the valuations produced directly by the models to reflect uncertainties in the relevant modeling assumptions and inputs used. In arriving at these estimates, UBS considers the range of market practice and how it believes other market participants would assess these uncertainties. Model reserves are periodically reassessed in light of information from market transactions, pricing utilities, and other relevant sources. The level of these model reserves is, nevertheless, to a large extent judgmental.

To estimate the potential effect on the Financial Statements from the use of alternative valuation techniques or assumptions, UBS makes use of the model reserve amounts described above, by scaling the level of the model reserves higher and lower, to assess the impact on valuation of increasing or decreasing the amount of model-related uncertainty considered.

The potential effect of using reasonably possible alternative valuation assumptions has been quantified as follows:

Scaling the model reserve amounts upward in line with less favorable assumptions would reduce fair value by approximately CHF 2,710 million at 31 December 2007, by approximately CHF 1,038 million at 31 December 2006 and approximately CHF 1,094 million at 31 December 2005.
Scaling the model reserve amounts downward in line with more favorable assumptions would increase fair value by approximately CHF 2,160 million at 31 December 2007, approximately CHF 955 million at 31 December 2006, and approximately CHF 1,176 million at 31 December 2005.