[["", "2005", "2006", "2007"], ["risk-free interest rate", "3.87% ( 3.87 % )", "4.14% ( 4.14 % )", "4.97% ( 4.97 % )"], ["expected option life ( in years )", "7.5", "7.3", "6.25"], ["expected volatility", "84% ( 84 % )", "73% ( 73 % )", "65% ( 65 % )"]]