and Other Contingencies

We are currently involved in various claims and legal proceedings. Quarterly, we review the status of each significant matter and assess our potential financial exposure. A description of our accounting policies associated with contingencies assumed as a part of a business combination is provided under “Business Combinations” above. For legal and other contingencies that are not a part of a business combination, we accrue a liability for an estimated loss if the potential loss from any claim or legal proceeding is considered probable and the amount can be reasonably estimated. Significant judgment is required in both the determination of probability and the determination as to whether the amount of an exposure is reasonably estimable. Because of uncertainties related to these matters, accruals are based only on the best information available at the time. As additional information becomes available, we reassess the potential liability related to our pending claims and litigation and may revise our estimates. Such revisions in the estimates of the potential liabilities could have a material impact on our results of operations and financial position.

Stock-Based Compensation

We account for share-based payments to employees, including grants of employee stock awards and purchases under employee stock purchase plans in accordance with ASC 718, Compensation—Stock Compensation, which requires that share-based payments (to the extent they are compensatory) be recognized in our consolidated statements of operations based on their fair values. In addition, we have applied certain of the provisions of the SEC’s guidance contained in ASC 718, in our accounting for stock-based compensation awards.

We are required to estimate the stock awards that we ultimately expect to vest and to reduce stock-based compensation expense for the effects of estimated forfeitures of awards over the expense recognition period. Although we estimate the rate of future forfeitures upon historical experience, actual forfeitures in the future may differ. In addition, to the extent our actual forfeitures are different than our estimates, we record a true-up for the difference in the period that the awards vest, and such true-ups could materially affect our operating results.

As required by ASC 718, we recognize stock-based compensation expense for share-based payments that are expected to vest. In determining whether an award is expected to vest, we use an estimated, forward-looking forfeiture rate based upon our historical forfeiture rates. Stock-based compensation expense recorded using an estimated forfeiture rate is updated for actual forfeitures quarterly. We also consider on a quarterly basis whether there have been any significant changes in facts and circumstances that would affect our expected forfeiture rate.

We estimate the fair values of employee stock options using a Black-Scholes-Merton valuation model. The fair value of an award is affected by our stock price on the date of grant as well as other assumptions including the estimated volatility of our stock price over the term of the awards and the estimated period of time that we expect