pre_text: awards . awards granted under the 2006 plan prior to december 5 , 2008 became fully vested and nonforfeitable upon the closing of the merger . 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 , 2009 , there were approximately 15.3 million shares of common stock reserved for future grants under the 2006 plan . stock options we use a lattice 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 , 2009 , 2008 and 2007 were $ 3.79 , $ 4.36 and $ 6.49 per option , respectively , which were calculated using the following weighted-average assumptions: .
post_text: republic services , inc . and subsidiaries notes to consolidated financial statements , continued .
table: 2009 2008 2007
table: Expected volatility 28.7% 27.3% 23.5%
table: Risk-free interest rate 1.4% 1.7% 4.8%
table: Dividend yield 3.1% 2.9% 1.5%
table: Expected life (in years) 4.2 4.2 4.0
table: Contractual life (in years) 7 7 7
table: Expected forfeiture rate 3.0% 3.0% 5.0%
question: Analyse this data from a financial earnings document. what was the percentage growth in the dividend yield from 2007 to 2008