A Canadian pension fund manager seeks to measure the sensitivity of her pension liabilities to market interest rate changes. The manager determines the present value of the liabilities under three interest rate scenarios: a base rate of 7%, a 100 bp increase in rates up to 8%, and a 100 bp drop in rates down to 6%. The results of the manager's analysis are presented below: Interest Rate Assumption Present Value of Liabilities CAD 510.1 million 6% 7% CAD 455.4 million 8% CAD 373.6 million The effective duration of the pension fund's liabilities is closest to