Are we in a housing bubble?

The term "bubble" means that prices are too high.  But the question is difficult to understand unless we know what to compare them to.  We can use the ideas of Chapter 9 to measure housing prices relative to the cost of renting.  Because renters can buy, and owners can sell and rent, in the long run the prices should be comparable (a mobile asset should be indifferent about where it is used).  Here is the Fed data on the relative costs of owning relative to renting.  

Many people (some economists) think that there was a housing bubble in 2006 whose bursting lead to the subsequent recession (shaded blue area).  Currently owning is 30% more expensive than renting.  In 2006, owning was 70% more expensive than renting.