In order to calculate and analyze the price index of real estate,we need to fully consider the influence of the changes in qualities and characteristics of the houses,and we should eliminate the factors of qualities and characteristics of the houses,so the price index of real estate can reflect the "pure" price changes in houses.

Under stochastic property of long term housing price, the economic implications of mortgage defaulting were discussed, the secondary partial derivative of mortgage pricing function was analyzed in detail, and an additional condition of defaulting was introduced.

However,the strangeness of index methodology frequently leads to the misunderstanding of the housing price index.

Research of real estate price index forecast based on wavelet neural network;

Real estate price index is a relative quantitative indicators that reflects the changes of the price in the real estate market in different periods,It s a so-called "pure price index".

By observing the movement of Real estate price index, people can grasp of the macro economic situation of the real estate market and the changes in the market, or from the micro level, people also can take an analysis according its investment trend, and the realization of these roles based on the analysis and forecast of real estate price index.