Straight from Schweser’s explanation of LOS 61c:
The cash flows and value of MBS are interest-rate-path-dependent, which means they must be valued with a Monte Carlo Model rather than a binomial model or any other model that employs the backward induction methodology. The cash flows for passthrough securities are a function of prepayment rates, and prepayment rates in any given month are affected by interest rates in the past. There are two sources of path dependency:
If mortgage rates trend downward over a period of time, prepayment rates will increase at the beginning of the trend as homeowners refinance their mortgages; but prepayments will slow as the trend continues, because many of the homeowners that can refinance will have already done so. This prepayment pattern is called prepayment burnout, and it applies to MBS and other types of passthrough security cash flows.
The cash flows that a particular tranche receives in any one month depend on the outstanding principal balances of the other tranches in the structure, which in turn depend on the prepayment history and the interest rate path.
The cash flows and value of MBS are interest-rate-path-dependent, which means they must be valued with a Monte Carlo Model rather than a binomial model or any other model that employs the backward induction methodology. The cash flows for passthrough securities are a function of prepayment rates, and prepayment rates in any given month are affected by interest rates in the past. There are two sources of path dependency:
If mortgage rates trend downward over a period of time, prepayment rates will increase at the beginning of the trend as homeowners refinance their mortgages; but prepayments will slow as the trend continues, because many of the homeowners that can refinance will have already done so. This prepayment pattern is called prepayment burnout, and it applies to MBS and other types of passthrough security cash flows.
The cash flows that a particular tranche receives in any one month depend on the outstanding principal balances of the other tranches in the structure, which in turn depend on the prepayment history and the interest rate path.