Dynamic Speculative Behaviors and Mortgage Bubbles

The real estate markets are full of speculative behaviors, and have been booming since the beginning of this decade. Even though the markets have only a very short history, the issue of how to rationally measure the speculative behaviors remains open in the academe and practice. Based on the levels of house prices, this booklet establishes some innovative dynamic models, proposes a concept of utilizing the ratio between net mortgage loan and net speculative gain to investigate the speculative behaviors and mortgage bubbles, and concludes some interesting results: The necessary condition of speculative behaviors' existence is that the growth rate of house prices must have a positive minimum boundary, and, the net mortgage loan to net speculative gain ratio subsequently exists, depicting approximately the potential risks banks would face. Furthermore, investor's behaviors may massively impact the trend of house prices through changing the expectation or variance of house returns in sale or in resale. The last finding indicates that investor's behaviors change markets' behaviors, which evidently testifies that the Efficient Market Hypothesis would be invalid.