Price-to-income ratios represent the amount borrowed relative to the incomes of the borrower. There are many variables that impact house prices, and some of the variability in prices over time can be attributed to changes in these variables; however, since most houses are purchased with lender financing, and since lender financing is linked to income, the price-to-income ratio is the best metric for evaluating long-term housing price trends. The price-to-income ratio does not need to be adjusted for inflation as both prices and income will rise with the general level of inflation. Most of the fluctuations in the ratio are based on changes in financing terms, in particular interest rates, and of course, irrational exuberance.



The Great Housing Bubble saw unprecedented price-to-income ratios because interest rates were at historic lows and the use of exotic financing including negative amortization loans were at historic highs. When measured against historic norms of house price to income, the degree of price inflation was staggering. In markets where bubble behavior is not prevalent, price to income ratios hover between 2.3 and 2.8. In bubble markets there is a tendency to maintain higher ratios, and the range over time is much greater. Any ratio less than 3 is generally considered affordable.

In bubble markets ratios of 3 to 4 are as affordable as they get. Anything greater than 4 is a strain on family budgets and generally a sign of an inflated market. Ratios greater than 5 are considered very unaffordable and prone to high rates of default because they tend to be characterized by exotic financing. Price-to-income ratios in the bubble of the early 90s in California did not exceed 6 because interest rates were higher and because negative amortization loans were not widely available. During the Great Housing Bubble, the national ratio of house price to income increased 30% from 4.0 to 5.2. This means 30% more debt is serviced by the same income. Some of this increased ability to service debt is explained by lower interest rates and exotic loan terms, and some of increase came from people choosing to take on larger debt loads due to the irrational expectation of ever increasing house prices coupled with loose lending standards which enabled the populace to take on these debts. The national trends were small compared to the frenzied activities of bubble markets in California where most markets saw their house price to income ratio double.

Buyers were never forced to buy; it was always a choice. During the market rally, greedy buyers motivated by rising prices and fueled by loose lending standards were able to bid prices up to ridiculous levels. The exotic financing was not a result of high prices; it was the cause of high prices. Lenders were keen to offer these products because they were not taking the risk, and it allowed them to keep transaction volumes high which is how they were making money. By late 2007, the market balance had shifted from favoring sellers to favoring buyers. The once greedy buyers were becoming desperate sellers: their dreams of riches from perpetual appreciation were in tatters. Many were forced to sell due to their inability to make their mortgage payments. Those that hung on were homeowners with 50% or more of their income going toward paying off an asset which was declining in value. It was not a set of circumstances to be envied.