pre_text: mastercard incorporated notes to consolidated financial statements 2014 ( continued ) ( in thousands , except percent and per share data ) upon termination of employment , excluding retirement , all of a participant 2019s unvested awards are forfeited . however , when a participant terminates employment due to retirement , the participant generally retains all of their awards without providing additional service to the company . eligible retirement is dependent upon age and years of service , as follows : age 55 with ten years of service , age 60 with five years of service and age 65 with two years of service . compensation expense is recognized over the shorter of the vesting periods stated in the ltip , or the date the individual becomes eligible to retire . there are 11550 shares of class a common stock reserved for equity awards under the ltip . although the ltip permits the issuance of shares of class b common stock , no such shares have been reserved for issuance . shares issued as a result of option exercises and the conversions of rsus are expected to be funded with the issuance of new shares of class a common stock . stock options the fair value of each option is estimated on the date of grant using a black-scholes option pricing model . the following table presents the weighted-average assumptions used in the valuation and the resulting weighted- average fair value per option granted for the years ended december 31: .
post_text: the risk-free rate of return was based on the u.s . treasury yield curve in effect on the date of grant . the company utilizes the simplified method for calculating the expected term of the option based on the vesting terms and the contractual life of the option . the expected volatility for options granted during 2009 was based on the average of the implied volatility of mastercard and a blend of the historical volatility of mastercard and the historical volatility of a group of companies that management believes is generally comparable to mastercard . the expected volatility for options granted during 2008 was based on the average of the implied volatility of mastercard and the historical volatility of a group of companies that management believes is generally comparable to mastercard . as the company did not have sufficient publicly traded stock data historically , the expected volatility for options granted during 2007 was primarily based on the average of the historical and implied volatility of a group of companies that management believed was generally comparable to mastercard . the expected dividend yields were based on the company 2019s expected annual dividend rate on the date of grant. .
table: 2009 2008 2007
table: Risk-free rate of return 2.5% 3.2% 4.4%
table: Expected term (in years) 6.17 6.25 6.25
table: Expected volatility 41.7% 37.9% 30.9%
table: Expected dividend yield 0.4% 0.3% 0.6%
table: Weighted-average fair value per option granted $71.03 $78.54 $41.03
question: Analyse this data from a financial earnings document. what was the percent of the change in the risk-free rate of return from 2008 to 2009