Please answer the given financial question based on the context.
Context: 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: .
||2010|2009|2008|
|expected volatility|28.6% ( 28.6 % )|28.7% ( 28.7 % )|27.3% ( 27.3 % )|
|risk-free interest rate|2.4% ( 2.4 % )|1.4% ( 1.4 % )|1.7% ( 1.7 % )|
|dividend yield|2.9% ( 2.9 % )|3.1% ( 3.1 % )|2.9% ( 2.9 % )|
|expected life ( in years )|4.3|4.2|4.2|
|contractual life ( in years )|7|7|7|
|expected forfeiture rate|3.0% ( 3.0 % )|3.0% ( 3.0 % )|3.0% ( 3.0 % )|
republic services , inc . notes to consolidated financial statements , continued .
Question: from 2009 to 2010 what was the percentage change in the expected volatility


Answer: The answer is:0.05128