matched to the portion of our net investment at risk. Accordingly, the variability involved in net investment hedges is substantially less than that of other types of hedge transactions and we do not expect any material ineffectiveness. We consider, on a quarterly basis, the need to redesignate existing hedge relationships based on changes in the underlying net investment. Should the level of our net investment decrease below hedged levels, any resulting ineffectiveness would be reported directly to earnings in the period incurred.

Stock−based Compensation

We account for stock−based compensation by estimating the fair value of stock−based compensation on the date of grant using the Black−Scholes option pricing model. The Black−Scholes option pricing model requires the input of highly subjective assumptions including volatility. Expected volatility is estimated based on implied volatility in market traded options on our common stock with a term greater than one year, along with other factors. Our decision to use implied volatility was based on the availability of actively traded options on our common stock and our assessment that implied volatility is more representative of future stock price trends than historical volatility. If factors change and we use different assumptions for estimating stock−based compensation expense in future periods, stock−based compensation expense may differ materially in the future from that recorded in the current period.

Taxes

We record valuation allowances against our deferred tax assets, when necessary. Realization of deferred tax assets (such as net operating loss carry−forwards) is dependent on future taxable earnings and is therefore uncertain. At least quarterly, we assess the likelihood that our deferred tax asset balance will be recovered from future taxable income. To the extent we believe that recovery is not likely, we establish a valuation allowance against our deferred tax asset, which increases our income tax expense in the period when such determination is made.

In addition, we have not recorded U.S. income tax expense for foreign earnings that we have determined to be indefinitely reinvested offshore, thus reducing our overall income tax expense. The amount of earnings designated as indefinitely reinvested offshore is based upon the actual deployment of such earnings in our offshore assets and our expectations of the future cash needs of our U.S. and foreign entities. Income tax considerations are also a factor in determining the amount of foreign earnings to be indefinitely reinvested offshore.

We carefully review all factors that drive the ultimate disposition of foreign earnings determined to be reinvested offshore, and apply stringent standards to overcoming the presumption of repatriation. Despite this approach, because the determination involves our future plans and expectations of future events, the possibility exists that amounts declared as indefinitely reinvested offshore may ultimately be repatriated. For instance, the actual cash needs of our U.S. entities may exceed our current expectations, or the actual cash needs of our foreign entities may be less than our current