It isn't enough to compare the spread to its average, Mr. Fridson says, because the average doesn't reflect the current level of default risk, the strength of the economy, the yield on government bonds or the availability of credit.

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Stock market strength and a higher 30-Year bond yield have pushed down equity valuations.

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Because of stock market strength and a higher 30-Year bond yield, equity valuations are less undervalued and more overvalued.

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Technically, a high yield test would be self-evidently a sign of national strength.

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But Ahrens expects the stock to rebound on the strength of its finances and its 5.9% dividend yield.

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The strength in stocks and the bullish economic readings sucked some of the steam out of bonds, with the yield on the 10-year U.S. Treasury note sailing higher up near 3.16%, up from 2.85% less than one week ago.

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