Read the following texts and table with financial data from an S&P 500 earnings report carefully.Based on the question-answer history (if provided), answer the last question. The answer may require mathematical calculation based on the data provided.


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: . <table class='wikitable'><tr><td>1</td><td>-</td><td>2010</td><td>2009</td><td>2008</td></tr><tr><td>2</td><td>expected volatility</td><td>28.6% ( 28.6 % )</td><td>28.7% ( 28.7 % )</td><td>27.3% ( 27.3 % )</td></tr><tr><td>3</td><td>risk-free interest rate</td><td>2.4% ( 2.4 % )</td><td>1.4% ( 1.4 % )</td><td>1.7% ( 1.7 % )</td></tr><tr><td>4</td><td>dividend yield</td><td>2.9% ( 2.9 % )</td><td>3.1% ( 3.1 % )</td><td>2.9% ( 2.9 % )</td></tr><tr><td>5</td><td>expected life ( in years )</td><td>4.3</td><td>4.2</td><td>4.2</td></tr><tr><td>6</td><td>contractual life ( in years )</td><td>7</td><td>7</td><td>7</td></tr><tr><td>7</td><td>expected forfeiture rate</td><td>3.0% ( 3.0 % )</td><td>3.0% ( 3.0 % )</td><td>3.0% ( 3.0 % )</td></tr></table> republic services , inc . notes to consolidated financial statements , continued .
Question: what is the expected volatility in 2009?
Answer: 28.7
Question: what about in 2008?

27.3