We review our investment portfolio for potential “other-than-temporary” declines in value on an individual investment basis. We assess, on a quarterly basis, significant declines in value which may be considered other-than- temporary and, if necessary, recognize and record the appropriate charge to write-down the carrying value of such  investments. In making this assessment, we take into consideration qualitative and quantitative information, including  but not limited to the following: the magnitude and duration of historical declines in market prices, credit rating activity,  assessments of liquidity, public filings, and statements made by the issuer. We generally begin our identification of potential other-than-temporary impairments by reviewing any security with a fair value that has declined from its original or adjusted cost basis by 25% or more for six or more consecutive months. We then evaluate the individual security based on the previously identified factors to determine the amount of the write-down, if any. As a result of our  review, we recorded an other-than-temporary impairment charge of $11 thousand during the fourth quarter of 2013.  For the years ended December 31, 2013, 2012 and 2011, we recorded charges of $25 thousand, $0.7 million and $68  thousand, respectively, related to the other-than-temporary impairment of certain publicly traded equity securities and  our deferred compensation plan assets. Actual losses, if any, could ultimately differ from these estimates. Future adverse  changes in market conditions or poor operating results of underlying investments could result in additional losses that  may not be reflected in an investment’s current carrying value, thereby possibly requiring an impairment charge in the future. See Note 4 of Notes to the Consolidated Financial Statements in this report for more information about our investments. We also invest in privately held entities and private equity funds and record these investments at cost. We review these investments periodically in order to determine if circumstances (both financial and non-financial) exist that indicate that we will not recover our initial investment. Impairment charges are recorded on investments having a cost  basis that is greater than the value that we would reasonably expect to receive in an arm’s length sale of the investment.  We have not been required to record any impairment losses relating to these investments in 2013, 2012 or 2011. n For purposes of determining the estimated fair value of our stock option awards on the date of grant, we use the Black-Scholes Model. This model requires the input of certain assumptions that require subjective judgment. These  assumptions include, but are not limited to, expected stock price volatility over the term of the awards and actual and  projected employee stock option exercise behaviors. Because our stock option awards have characteristics significantly  different from those of traded options, and because changes in the input assumptions can materially affect the fair value  estimate, the existing model may not provide a reliable single measure of the fair value of our stock option awards. For purposes of determining the estimated fair value of our performance-based restricted stock unit awards on the date of grant, we use a Monte Carlo Simulation valuation method. The restricted stock units are subject to a market condition based on the relative total shareholder return of ADTRAN against all of the companies in the NASDAQ Telecommunications Index and vest at the end of a three-year performance period. The fair value of restricted stock issued to our Directors is equal to the closing price of our stock on the date of grant. Management will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. Circumstances may change and additional data may become available over time, which could result in changes to these assumptions and methodologies and thereby materially impact our fair value determination. If factors change in future periods, the compensation expense that we record may differ significantly from what we have recorded in the current period.  n We estimate our income tax provision or benefit in each of the jurisdictions in which we operate, including estimating  exposures related to examinations by taxing authorities. We also make judgments regarding the realization of deferred tax assets, and establish valuation allowances where we believe it is more likely than not that future taxable income in  certain jurisdictions will be insufficient to realize these deferred tax assets. Our estimates regarding future taxable income  and income tax provision or benefit may vary due to changes in market conditions, changes in tax laws, or other factors.  If our assumptions, and consequently our estimates, change in the future, the valuation allowances we have established  may be increased or decreased, impacting future income tax expense. At December 31, 2013 and 2012 respectively, the  valuation allowance was $8.8 million and $10.9 million. As of December 31, 2013, we have state research tax credit carry-forwards of $3.6 million, which will expire between 2015 and 2028. These carry-forwards were caused by tax ADTRAN 2013 Annual Report 20