Please answer the given financial question based on the context.
Context: 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: .
||2009|2008|2007|
|risk-free rate of return|2.5% ( 2.5 % )|3.2% ( 3.2 % )|4.4% ( 4.4 % )|
|expected term ( in years )|6.17|6.25|6.25|
|expected volatility|41.7% ( 41.7 % )|37.9% ( 37.9 % )|30.9% ( 30.9 % )|
|expected dividend yield|0.4% ( 0.4 % )|0.3% ( 0.3 % )|0.6% ( 0.6 % )|
|weighted-average fair value per option granted|$ 71.03|$ 78.54|$ 41.03|
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. .
Question: what is the variation observed in the risk-free rate of return during 2008 and 2009?


Answer: The answer is:0.007