Warren Buffett's and Robert Shiller's stock valuation metrics agree

Carol Loomis of Fortune has a new article out saying that Warren Buffett's valuation metric says it's time to buy stocks. I decided to compare Warren Buffett's stock valuation metric with Robert Shiller's. They both compare nicely.

Warren Buffett's stock valuation metric: Total stock market value as a percent of GNP.

Yale economist Robert Shiller's stock valuation metric, based on Benjamin Graham's advice in Security Analysis: S&P 500 10-year price/earnings ratios.

Robert Shiller doesn't compare the S&P 500 only to its current year earnings. Instead, he compares it to the average of the past ten years, adjusted for inflation. This way, he avoids getting fooled when single-year corporate earnings rise and fall with the business cycle.

Although Warren Buffett's and Robert Shiller's valuation methods are entirely different, they both seem to track each other fairly nicely. Knowing what happened in 1929, however, it looks like Robert Shiller's valuation method is slightly better than Warren Buffett's.