House price run-ups, especially when they appear excessive, are difficult to explain. It is it even more difficult to explain how they are not coordinated across countries in a globalized world. Indeed, right now house prices are severely depressed in the United States, while you can have strong suspicions of bubbles in China, Norway and Switzerland. Bubbles are substantial deviations from fundamentals that could be due to some deviations from rationality or herd behavior, or both. But "rationalizing" this is a major challenge because of the apparent randomness of the occurrence of such house price booms.
Klaus Adam, Pei Kuang and Albert Marcet think they have a way to explain this using the concept of internally rationally agent. Such a agent, like the economist, does not know the true process of prices but tries to infer it from past observation using Bayes' rule. The belief about prices then becomes part of the state space and leads to some sort of path dependence. With shocks that are not perfectly correlated, it is then possible for different countries to experience different paths for house prices.