Income and demographics are the other two critical factors which determine the demand for housing. The change of their growth rate brings about demand shock for housing market directly. When the PCDI (per capita dis- posable income) or the growth rate of urban population increase, the demand for housing rises and the vacancy rate declines while rent and house prices continue to rise. But because the short-term supply is inelastic, house prices rise. When the supply is surplus, market situation will turn out to be worse combined with the fluctuation of economic periods.