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: .

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 | 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
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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 average expected volatility for the years 2007-2009?
Program: table_average(expected volatility, none)
Answer: 0.36833