why the smaller housing bubble was so much painful than the larger dot-com bubbles

From Stephen Gjerstad and Vernon Smith in the WSJ...

Smith won the Nobel Prize in Economics for his work in experimental economics, while at George Mason University in 2002.

Bubbles have been frequent in economic history, and they occur in the laboratories of experimental economics under conditions which -- when first studied in the 1980s -- were considered so transparent that bubbles would not be observed.

We economists were wrong: Even when traders in an asset market know the value of the asset, bubbles form dependably. Bubbles can arise when some agents buy not on fundamental value, but on price trend or momentum. If momentum traders have more liquidity, they can sustain a bubble longer.

But what sparks bubbles? Why does one large asset bubble -- like our dot-com bubble -- do no damage to the financial system while another one leads to its collapse? Key characteristics of housing markets -- momentum trading, liquidity, price-tier movements, and high-margin purchases -- combine to provide a fairly complete, simple description of the housing bubble collapse, and how it engulfed the financial system and then the wider economy....

In just the past 40 years there were two other housing bubbles, with peaks in 1979 and 1989, but the largest one in U.S. history started in 1997, probably sparked by rising household income that began in 1992 combined with the elimination in 1997 of taxes on residential capital gains up to $500,000. Rising values in an asset market draw investor attention; the early stages of the housing bubble had this usual, self-reinforcing feature.

The 2001 recession might have ended the bubble, but the Federal Reserve decided to pursue an unusually expansionary monetary policy in order to counteract the downturn....Both the Clinton and Bush administrations aggressively pursued the goal of expanding homeownership, so credit standards eroded. Lenders and the investment banks that securitized mortgages used rising home prices to justify loans to buyers with limited assets and income. Rating agencies accepted the hypothesis of ever rising home values, gave large portions of each security issue an investment-grade rating, and investors gobbled them up.

But housing expenditures in the U.S. and most of the developed world have historically taken about 30% of household income. If housing prices more than double in a seven-year period without a commensurate increase in income, eventually something has to give....

Monetary policy, mortgage finance, relaxed lending standards, and tax-free capital gains provided astonishing economic stimulus: Mortgage loan originations increased an average of 56% per year for three years -- from $1.05 trillion in 2000 to $3.95 trillion in 2003!...

In one city after another, prices of homes in the low-price tier appreciated the most and then fell the most; prices in the high-priced tier appreciated least and fell the least....

How can one crash that wipes out $10 trillion in assets cause no damage to the financial system and another that causes $3 trillion in losses devastate the financial system?

In the equities-market downturn early in this decade, declining assets were held by institutional and individual investors that either owned the assets outright, or held only a small fraction on margin, so losses were absorbed by their owners. In the current crisis, declining housing assets were often, in effect, purchased between 90% and 100% on margin....

In an important paper in 1983, Ben Bernanke argued that during the Depression, severe damage to the financial system impeded its ability to perform its economic role of lending to households for durable goods consumption and to firms for production and trade. We are seeing this process playing out now as loan funds for automobile purchases have withered....

The events of the past 10 years have an eerie similarity to the period leading up to the Great Depression. Total mortgage debt outstanding increased from $9.35 billion in 1920 to $29.44 billion in 1929. In 1920, residential mortgage debt was 10.2% of household wealth; by 1929, it was 27.2% of household wealth.

The Great Depression has been attributed to excessive speculation on Wall Street, especially between the spring of 1927 and the fall of 1929. Had the difficulties of the banking system been caused by losses on brokers' loans for margin purchases in 1929, the results should have been felt in the banks immediately after the stock market crash. But the banking system did not show serious strains until the fall of 1930....

The causes of the Great Depression need more study, but the claims that losses on stock-market speculation and a monetary contraction caused the decline of the banking system both seem inadequate. It appears that both the Great Depression and the current crisis had their origins in excessive consumer debt -- especially mortgage debt -- that was transmitted into the financial sector during a sharp downturn....

The hypothesis we propose is that a financial crisis that originates in consumer debt, especially consumer debt concentrated at the low end of the wealth and income distribution, can be transmitted quickly and forcefully into the financial system.