In 1988, he got attracted to International Dairy Queen and bought 50 shares of its class A stock mainly because he thought it was a company that Buffett would favor, given its good products, easy-to-understand operations, high returns on equity, little debt, and a reasonable price-earnings ratio.

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In the past, levels of 23 or so on this "Shiller Price-to-Earnings Ratio" have almost always been followed by poor returns over the subsequent decade, according to research by Prof.

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The ratio, devised by a Nobel-prize winning economist, looks at the relationship between investment returns and their variability.

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