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Robert Shiller
Robert Shiller
The Yale professor and co-founder of MacroMarkets called both the dot-com and housing bubbles.

We don't currently have anywhere near the level of unemployment that we had in the 1930s, but otherwise there are many similarities between today's environment and the Great Depression, with things happening today that we haven't seen since then. First of all, there's the magnitude of the stock market's move up and down. The real (inflation-corrected) value of the S&P 500 nearly tripled from 1995 to 2000, and by November 2008 was down nearly 60% from its 2000 peak. The only other comparable event was the one in the 1920s where real stock prices more than tripled from 1924 to 1929 and then fell 80% from 1929 to 1932. Second, we've had the biggest housing bust since the Depression. Third, we've seen 0% interest rates. We've actually seen briefly negative short-term interest rates. That hasn't happened since 1941. There was a period from 1938 to 1941 when we were bouncing around at zero and sometimes negative, but that hasn't happened since.

And the list goes on: Our numbers don't go back as far as the Depression, but consumer confidence is plausibly at the lowest level since then. Volatility of the stock market in terms of percentage changes day-to-day is the highest since the Depression. In October 2008 we saw the biggest drop in consumer prices in one month since April 1938. Another thing is that it's a worldwide event, as it was in the Depression.

I'm optimistic that we'll do better this time, but I'm worried that we're vulnerable. One of the lessons from the Depression is that things can smolder for a long time. What I'm worried about right now is that our confidence has been hurt, and that's difficult to restore. No matter what we do, we're trying to deal with a psychological phenomenon. So the Fed can cut interest rates and purchase asset-backed securities, but that only works in really restoring full prosperity if people believe that we're back again. That's a little hard to manage.

In terms of the stock market, the price/earnings ratio is no longer high. I use a P/E ratio in which the price is divided by ten-year average earnings. It's a really conservative way of looking at it. That P/E ratio got up to 44 in the year 2000, which was a record high. Recently it was down to less than 13, which is below the average of around 15. But after the stock market crash of 1929, the price/earnings ratio got down to about six, which is less than half of where it is now. So that's the worry. Some people who are so inclined might go more into the market here because there's a real chance it will go up a lot. But that's very risky. It could easily fall by half again.

NEXT: Sheila Bair
Last updated December 11 2008: 7:04 PM ET
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