[["", "2009", "2008", "2007"], ["weighted-average fair value at grant date", "$ 14.24", "$ 17.95", "$ 21.07"], ["expected option life ( years )", "4.6", "5.1", "4.8"], ["expected volatility", "39.2% ( 39.2 % )", "28.2% ( 28.2 % )", "28.9% ( 28.9 % )"], ["risk-free interest rate at grant date", "1.9% ( 1.9 % )", "2.9% ( 2.9 % )", "4.5% ( 4.5 % )"], ["dividend yield", "none", "none", "none"]]