american tower corporation and subsidiaries notes to consolidated financial statements assessments in each of the tax jurisdictions resulting from these examinations .
the company believes that adequate provisions have been made for income taxes for all periods through december 31 , 2010 .
12 .
stock-based compensation the company recognized stock-based compensation of $ 52.6 million , $ 60.7 million and $ 54.8 million for the years ended december 31 , 2010 , 2009 and 2008 , respectively .
stock-based compensation for the year ended december 31 , 2009 included $ 6.9 million related to the modification of the vesting and exercise terms for certain employee 2019s equity awards .
the company did not capitalize any stock-based compensation during the years ended december 31 , 2010 and 2009 .
summary of stock-based compensation plans 2014the company maintains equity incentive plans that provide for the grant of stock-based awards to its directors , officers and employees .
under the 2007 equity incentive plan ( 201c2007 plan 201d ) , which provides for the grant of non-qualified and incentive stock options , as well as restricted stock units , restricted stock and other stock-based awards , exercise prices in the case of non-qualified and incentive stock options are not less than the fair market value of the underlying common stock on the date of grant .
equity awards typically vest ratably over various periods , generally four years , and generally expire ten years from the date of grant .
stock options 2014as of december 31 , 2010 , the company had the ability to grant stock-based awards with respect to an aggregate of 22.0 million shares of common stock under the 2007 plan .
the fair value of each option grant is estimated on the date of grant using the black-scholes option pricing model based on the assumptions noted in the table below .
the risk-free treasury rate is based on the u.s .
treasury yield in effect at the accounting measurement date .
the expected life ( estimated period of time outstanding ) was estimated using the vesting term and historical exercise behavior of company employees .
the expected volatility was based on historical volatility for a period equal to the expected life of the stock options .
key assumptions used to apply this pricing model are as follows: .

2010
2009
2008
Range of risk-free interest rate
1.41% – 2.39%
1.41% – 2.04%
1.44% – 3.05%
Weighted average risk-free interest rate
2.35%
1.71%
1.89%
Expected life of option grants
4.60 years
4.00 years
4.00 years
Range of expected volatility of underlying stock price
37.11% – 37.48%
36.00% – 36.63%
28.51% – 35.30%
Weighted average expected volatility of underlying stock price
37.14%
36.23%
29.10%
Expected annual dividends
N/A
N/A
N/A

the weighted average grant date fair value per share during the years ended december 31 , 2010 , 2009 and 2008 was $ 15.03 , $ 8.90 and $ 9.55 , respectively .
the intrinsic value of stock options exercised during the years ended december 31 , 2010 , 2009 and 2008 was $ 62.7 million , $ 40.1 million and $ 99.1 million , respectively .
as of december 31 , 2010 , total unrecognized compensation expense related to unvested stock options was approximately $ 27.7 million and is expected to be recognized over a weighted average period of approximately two years .
the amount of cash received from the exercise of stock options was approximately $ 129.1 million during the year ended december 31 , 2010 .
during the year ended december 31 , 2010 , the company realized approximately $ 0.3 million of state tax benefits from the exercise of stock options. .

Question: Analyse this data from a financial earnings document. what was the percent of the change in the weighted average risk-free interest rate
Choices:
-10.32164
1.97573
1.70758
1
0.37427
Correct choice index: 4