[["", "2007", "2006", "2005"], ["range of risk free interest rates", "4.98% ( 4.98 % ) 20145.05% ( 20145.05 % )", "5.01% ( 5.01 % ) 20145.17% ( 20145.17 % )", "3.17% ( 3.17 % ) 20144.30% ( 20144.30 % )"], ["weighted average risk-free interest rate", "5.02% ( 5.02 % )", "5.08% ( 5.08 % )", "3.72% ( 3.72 % )"], ["expected life of the shares", "6 months", "6 months", "6 months"], ["range of expected volatility of underlying stock price", "27.5% ( 27.5 % ) 201428.7% ( 201428.7 % )", "29.6% ( 29.6 % )", "29