Despite valuation concerns, stocks haven't been this cheap since the 1950s by one metric

A trader works on the floor of the New York Stock Exchange shortly after the opening bell in New York, January 24, 2020.
Lucas Jackson | Reuters

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Concerns about market valuation have risen after dire warnings from notable investors, including Stanley Druckenmiller and David Tepper, but going by one measure, stocks haven't been this attractive in 70 years, according to Bank of America.