MBS are the most complicated securities that are sensitive to interest rates. The factors that affect the price of MBS are varied and most of them are difficult to model to an accurate degree. Though prepayment behavior is an essential part of any MBS, it actually depends on the economic conditions and the present level of interest rates.  Low interest rates may induce borrowers to prepay the mortgage so that they can refinance their property at a lower rate. However, in case of a mortgage pool, each and every house/property owner may prepay when the call option is in the money. In such case, the interest rate is related to the tendency to prepay. Generally, the share of mortgage that is prepaid in a period is inversely related to the level of interest rates.