For all time periods from i=2 to i=M, bootstrapping is applied, using the following formula to determine di: d i = 1 - C i ??? ??? j = 1 i - 1 ??? A j ??? d j 1 + A i ??? C i , ( 2 ) where j is a positive integer, and Ai and Aj are the accrual factors in time period i and j, respectively.