An analyst uses the following binomial interest rate tree to examine the interest rate sensitivity of a 2-year, 4% annual coupon bond callable in one year at par, with a current price of 99.6345:

Year 0          Year 1
---             4.7967%
4.0000%         ---
---             3.2153%

Year 0          Year 1
---             4.7967%
4.0000%         ---
---             3.2153%

If she estimates the price of the bond to be 98.9323 if the benchmark yield curve increases by 50 bps, the effective duration of the bond is closest to: