cash flows involve businesses and geographies with limited financial history and developing revenue models. Changes in these forecasts could significantly change the amount of impairment recorded, if any. 

During the year, management monitored the actual performance of the business relative to the fair value assumptions used during our annual goodwill impairment test. For the periods presented, no triggering events were identified that required an update to our annual impairment test. As a measure of sensitivity, a 10% decrease in the fair value of any of our reporting units as of December 31, 2012 would have had no impact on the carrying value of our goodwill. 

Financial and credit market volatility directly impacts our fair value measurement through our weighted average cost of capital that we use to determine our discount rate and through our stock price that we use to determine our market capitalization. During times of volatility, significant judgment must be applied to determine whether credit or stock price changes are a short-term swing or a longer-term trend. As a measure of sensitivity, a prolonged 20% decrease from our December 31, 2012, closing stock price would not be an indicator of possible impairment. 

Stock-Based Compensation 

We measure compensation cost for stock awards at fair value and recognize it as compensation expense over the service period for awards expected to vest. The fair value of restricted stock units is determined based on the number of shares granted and the quoted price of our common stock. The estimation of stock awards that will ultimately vest requires judgment for the amount that will be forfeited, and to the extent actual results or updated estimates differ from our current estimates, such amounts will be recorded as a cumulative adjustment in the period estimates are revised. We consider many factors when estimating expected forfeitures, including employee class, economic environment, and historical experience. We update our estimated forfeiture rate quarterly. A 1% change to our estimated forfeiture rate would have had an approximately $22 million impact on our 2012 operating income. Our estimated forfeiture rates at December 31, 2012 and 2011, were 27% and 28%. 

We utilize the accelerated method, rather than the straight-line method, for recognizing compensation expense. For example, over 50% of the compensation cost related to an award vesting ratably over four years is expensed in the first year. If forfeited early in the life of an award, the compensation expense adjustment is much greater under an accelerated method than under a straight-line method. 

Income Taxes 

We are subject to income taxes in the U.S. and numerous foreign jurisdictions. Significant judgment is required in evaluating and estimating our provision and accruals for these taxes. During the ordinary course of business, there are many transactions for which the ultimate tax determination is uncertain. Our effective tax rates could be adversely affected by earnings being lower than anticipated in countries where we have lower statutory rates and higher than anticipated in countries where we have higher statutory rates, by