rate.

 

We estimate the fair value of employee stock options using a Black-Scholes 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 employees to hold their stock options. The risk-free interest rate assumption we use is based upon United States treasury interest rates appropriate for the expected life of the awards. We use the implied volatility of our publicly traded, longest-term options in order to estimate future stock price trends as we believe that implied volatility is more representative of future stock price trends than historical volatility. In order to determine the estimated period of time that we expect employees to hold their stock options, we have used historical rates of employee groups by seniority of job classification. Our expected dividend rate was zero prior to our first dividend declaration in the fourth quarter of fiscal 2009 as we did not historically pay cash dividends on our common stock and did not anticipate doing so for the foreseeable future for grants issued prior to this declaration date. For grants issued subsequent to this dividend declaration date, we used an annualized dividend yield based on the per share dividend declared by our Board of Directors. The aforementioned inputs entered into the option valuation model we use to fair value our stock awards are subjective estimates and changes to these estimates will cause the fair value of our stock awards and related stock-based compensation expense we record to vary.

 

We record deferred tax assets for stock-based awards that result in deductions on our income tax returns, based on the amount of stock-based compensation recognized and the statutory tax rate in the jurisdiction in which we will receive a tax deduction. Because the deferred tax assets we record are based upon the stock-based compensation expenses in a particular jurisdiction, the aforementioned inputs that affect the fair value of our stock awards may also indirectly affect our income tax expense. In addition, differences between the deferred tax assets recognized for financial reporting purposes and the actual tax deduction reported on our income tax returns are recorded in additional paid-in capital. If the tax deduction is less than the deferred tax asset, such shortfalls reduce our pool of excess tax benefits. If the pool of excess tax benefits is reduced to zero, then subsequent shortfalls would increase our income tax expense. Our pool of excess tax benefits is computed in accordance with the alternative transition method as prescribed under FASB Staff Position FAS 123R-3, Transition Election to Accounting for the Tax Effects of Share-Based Payment Awards .

 

To the extent we change the terms of our employee stock-based compensation programs, experience market volatility in the pricing of our common stock that increases the implied volatility calculation of our publicly traded, longest-term options or refine different assumptions in future periods such as forfeiture rates that