PART I Allowance for Doubtful Accounts  Estimated Useful Lives of Long-Lived Assets  Investments in Unconsolidated Companies  70 We maintain allowances for doubtful accounts for estimated losses that result from the inability of our  customers to make required payments. We base our allowances on the likelihood of recoverability of accounts  receivable by operating segment based on past experience and current collection trends that we expect to  continue. Our evaluation also includes the length of time the receivables are past due, geographic concentrations  and the general business environment. If changes in these factors occur, or the historical data we use to calculate  the allowance provided for doubtful accounts does not reflect the future ability to collect outstanding receivables,  additional provisions for doubtful accounts may be needed and our future results of operations could be  materially and adversely affected. Even as revenues have increased in recent years, the allowance for doubtful  accounts has decreased due to stricter credit investigations for new customers and more efficient collection  activities for outstanding accounts.  A significant portion of our total assets consists of long-lived assets, primarily property, plant and equipment  and definite-lived intangibles. We estimate the useful lives of property, plant and equipment and other long-lived  assets with finite lives in order to determine the period of time over which depreciation and amortization expense  should be recorded. The useful lives are estimated at the time assets are acquired and are based on historical  experience with similar assets as well as the anticipated technological evolution or other environmental changes.  If technological changes were to occur more rapidly than anticipated or in a different form than anticipated,  the useful lives assigned to these assets may need to be shortened, resulting in the recognition of increased  depreciation and amortization in the relevant periods. Alternatively, technological obsolescence could result in  a write-down in the value of the assets to reflect impairment. We review these types of assets for impairment  quarterly, or when events or circumstances indicate that the carrying amount may not be recoverable over  the remaining life of an asset. In assessing impairments, we use estimated cash flows that take into account  management’s estimates of future operations. We did not have significant impairment losses of long-lived assets  in 2008 and 2009, but had NT$66 million (US$2.3 million) impairment loss in 2010.  We hold investments in other companies that we account for under the equity method or cost method of  accounting, depending on our ability to exert significant influence over the investee company. The amounts for  our equity method investments generally represent our cost of the initial investment adjusted for our share of  the investee company’s income or loss and any dividends received. The amounts for our investments carried at  cost where the securities are not publicly traded generally represent our cost of the initial investment less any  adjustments we make when we determine that an investment’s net realizable value is less than its carrying cost.  Estimating the net realizable value of investments in privately held companies can be inherently subjective and  may contribute to significant volatility in our reported results of operations.  We assess the impairment of investments accounted for using the equity method whenever triggering  events or changes in circumstances indicate that an investment may be impaired and carrying value may not be  recoverable. We measure the impairment based on the projected future cash flow of the investees, the underlying  assumptions for which had been formulated by such investees’ internal management team, taking into account  sales growth and capacity utilization.  The process of assessing whether a particular cost method investment’s net realizable value is less than its  carrying cost requires a significant amount of judgment. We periodically evaluate these long-term investments  based on quoted market prices, if available, the financial condition of the investee company, economic conditions  in the industry and our intent and ability to hold the investment for a long period of time. If quoted market prices  are not available, we estimate the fair value using the net asset values as well as the financial condition of the  investee company. This information may be based on information that we request from the investee companies  and may not be subject to the same disclosure and audit requirements as required of U.S. companies, and as such,  the reliability and accuracy of the information may vary. If we deem the fair value of an investment to be less  than the book value based on the above factors, and the decline in value is deemed to be other than temporary,  we record the difference as impairment in the period of occurrence. In 2008, we recognized impairment losses 