From a Motley Fool article :
In 2001 Buffett explained that determining whether the market is expensive or cheap doesn't have to be complicated. Here's the metric he uses:
The market value of all publicly traded securities as a percentage of the country's business -- that is, as a percentage of GNP. Basically, Buffett divides the total market capitalization of the U.S. stock market by gross national product. GNP measures the value of goods and services that a country's citizens produce regardless of where they live. This includes the value of goods and services that American companies produce abroad.
Buffett : "If the percentage relationship falls to the 70% or 80% area, buying stocks is likely to work very well for you. If the ratio approaches 200% -- as it did in 1999 and a part of 2000 -- you are playing with fire."
The most common way to calculate the market value is by looking up the market capitalization of the Wilshire 5000. The market cap of the Wilshire 5000 was $20.6 trillion. The Federal Reserve Bank of St. Louis has a great website where you can locate GNP ($16.9 trillion). (http://research.stlouisfed.org/fred2/series/GNP/)
Dividing the total market cap by GNP gives 122% indicates that the market is getting pricey.
-We don't spend any time looking back. We figure there is so much to look forward to, there's just no sense thinking of what might have been, it just doesn't make any difference. You can only live life forward. You can perhaps learn something from the mistakes
-Interest rate impact. What you really want to know in investments is what is important and what is knowable. If its unimportant or unknowable, you forget about it. We don't want to pass up a chance to do something intelligent because of some prediction that we're no good on anyway. So we don't read, or listen or do anything based on macro factors, zero.
-Concentrate on what will happen, not on the when. The when is unknowable.
