units. If the fair value is determined to be less than the book value or qualitative factors indicate that it is more likely than not that goodwill is impaired, a second step is performed to compute the amount of impairment as the difference between the estimated fair value of goodwill and the carrying value. We estimate the fair value of the reporting units using discounted cash flows. Forecasts of future cash flows are based on our best estimate of future net sales and operating expenses, based primarily on expected category expansion, pricing, market segment share, and general economic conditions. Certain estimates of discounted 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 interim impairment test. As a measure of sensitivity, a 10% decrease in the fair value of any of our reporting units as of December 31, 2014, 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 a 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 short-term in nature or a longer-term trend. We have not made any significant changes to the accounting methodology used to evaluate goodwill impairment. Changes in our estimated future cash flows and asset fair values may cause us to realize material impairment charges in the future. As a measure of sensitivity, a prolonged 20% decrease from our December 31, 2014 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 estimated number of stock awards that will ultimately vest requires judgment, 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 classification, economic environment, and historical experience. We update our estimated forfeiture rate quarterly. We have not made any significant changes to the accounting methodology used to evaluate stock-based compensation. Changes in our estimates and assumptions may cause us to realize material changes in stock-based compensation expense in the future. As a measure of sensitivity, a 1% change to our estimated