The Valuation of Pass-Through Mortgage-Backed Securities in Korean Market

Abstract

This paper introduces a basic model and an extended model to evaluate the pass-through mortgage-backed securities (MBS) recently issued by Korea Housing Finance Corporation. The basic model assumes that the processes of interest rates, prepayment rates, and option-adjusted spreads have simple forms, of which parameters can be easily estimated by the market data available today. This paper presents the pricing formula on the basic model and the demonstrations under the present market data. We also suggest an extended model, a new but complicated model for pricing pass-through MBS, in which the interest rates and prepayment rates follow stochastic processes, and the option-adjusted spread is decomposed into one from refinancing and the other from mortgage turnover. However, since this kind of pass-through MBS has been traded in Korean financial market only recently, the market parameters in the extended model are not able to be estimated properly. We, instead, develop the pricing formula under the extended model and present the process of estimation of the parameters of the model. The participants in Korean MBS market can price the pass-through MBS for now under the basic model with limited set of data available, and later, when the market data is accumulated enough to estimate the parameters properly, they can take advantage of the extended model.