pre_text: 2006 plan prior to december 5 , 2008 became fully vested and nonforfeitable upon the closing of the acquisition . awards may be granted under the 2006 plan , as amended and restated , after december 5 , 2008 only to employees and consultants of allied waste industries , inc . and its subsidiaries who were not employed by republic services , inc . prior to such date . at december 31 , 2010 , there were approximately 15.3 million shares of common stock reserved for future grants under the 2006 plan . stock options we use a binomial option-pricing model to value our stock option grants . we recognize compensation expense on a straight-line basis over the requisite service period for each separately vesting portion of the award , or to the employee 2019s retirement eligible date , if earlier . expected volatility is based on the weighted average of the most recent one-year volatility and a historical rolling average volatility of our stock over the expected life of the option . the risk-free interest rate is based on federal reserve rates in effect for bonds with maturity dates equal to the expected term of the option . we use historical data to estimate future option exercises , forfeitures and expected life of the options . when appropriate , separate groups of employees that have similar historical exercise behavior are considered separately for valuation purposes . the weighted-average estimated fair values of stock options granted during the years ended december 31 , 2010 , 2009 and 2008 were $ 5.28 , $ 3.79 and $ 4.36 per option , respectively , which were calculated using the following weighted-average assumptions: .
post_text: republic services , inc . notes to consolidated financial statements , continued .
table: 2010 2009 2008
table: Expected volatility 28.6% 28.7% 27.3%
table: Risk-free interest rate 2.4% 1.4% 1.7%
table: Dividend yield 2.9% 3.1% 2.9%
table: Expected life (in years) 4.3 4.2 4.2
table: Contractual life (in years) 7 7 7
table: Expected forfeiture rate 3.0% 3.0% 3.0%
question: Analyse this data from a financial earnings document. from 2009 to 2010 what was the percentage change in the expected volatility