Accounting for Share-Based Compensation Plans
July 31, 2013, there was $351 millionof total unrecognized compensation cost related to non-vested share-based compensation arrangements granted under all equity compensation plans which we will amortize to expense in the future. Total unrecognized compensation cost will be adjusted for future changes in estimated forfeitures. We expect to recognize that cost over a weighted average vesting period of 2.3 years. We use a lattice binomial model and the assumptions described in Note 12 to the financial statements in Item 8 of this Report to estimate the fair value of stock options granted. We estimate the expected term of options granted based on implied exercise patterns using a binomial model. We estimate the volatility of our common stock at the date of grant based on the implied volatility of publicly traded one-year and two-year options on our common stock. Our decision to use implied volatility is based upon 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. We base the risk-free interest rate that we use in our option valuation model on the implied yield in effect at the time of option grant on constant maturity U.S. Treasury issues with equivalent remaining terms. In fiscal 2012 we began paying quarterly cash dividends and as a result we began using an annualized expected dividend yield in our option valuation model. We estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. We use historical data to estimate pre-vesting option forfeitures and record share-based compensation expense only for those awards that are expected to vest. We amortize the fair value of options on a straight-line basis over the requisite service periods of the awards, which are generally the vesting periods. We may elect to use different assumptions under our option valuation model in the future, which could materially affect our net income or loss and net income or loss per share. Restricted stock units (RSUs) granted typically vest based on continued service. We value these time-based RSUs at the date of grant using the intrinsic value method, adjusted for estimated forfeitures. We amortize the fair value of time-based RSUs on a straight-line basis adjusted for estimated forfeitures over the service period. Certain RSUs granted to senior management vest based on the achievement of pre-established performance or market goals. We estimate the fair value of performance-based RSUs at the date of grant using the intrinsic value method and the probability that the specified performance criteria will be met, adjusted for estimated forfeitures. Each quarter we update our assessment of the probability that the specified performance criteria will be achieved and adjust our estimate of the fair value of the performance-based RSUs if necessary. We amortize the fair values of performance-based RSUs over the requisite service period adjusted for estimated forfeitures for each separately vesting tranche of the award. We estimate the fair value of market-based RSUs at the date of grant using a Monte Carlovaluation methodology and amortize those fair values over the requisite service period adjusted for estimated forfeitures for each separately vesting tranche of the award. The Monte Carlomethodology that we use to estimate the fair value of market-based RSUs at the date of grant incorporates into the valuation the possibility that the market condition may not be satisfied.