(Bloomberg News) Valuations for U.S. equities have been stuck below the five-decade average for the longest period since Richard Nixon's presidency, a sign investors don't trust earnings even after a three-year bull market.

Analysts estimate profits in the Standard & Poor's 500 Index will reach a record $104.78 this year after increasing 125 percent since the end of 2009, the fastest expansion in a quarter century, according to data compiled by Bloomberg. American companies are boosting income so much that even after stocks doubled, the S&P 500 hasn't traded above its 16.4 mean ratio for 446 days, the longest stretch since the 13 years beginning in 1973.

Battered by the 14 percent decline in the S&P 500 since 2000, the worst financial crisis since the Great Depression and the so-called flash crash 21 months ago, investors are staying away from stocks, even after record profits, 10 quarters of U.S. economic growth and promises by the Federal Reserve to keep interest rates near zero through 2014. Of the $37 trillion erased from global equities in the credit crisis, $24 trillion has been restored.

"After two significant bear markets, the flash crash and the lost decade, many have simply said, 'No mas,'" Howard Ward, who helps oversee $35 billion at Gamco Investors Inc. in Rye, New York, said in an e-mail on Jan. 24. "Of course, bull markets have a history of climbing a wall of worry. And it is happening again."

The Fed's pledge to keep interest rates low through 2014 helped send the S&P 500 up 0.1 percent to 1,316.33 last week and extended its 2012 advance to 4.7 percent, the best start to a year since 1989. At the same time, an average of 6.69 billion shares traded on U.S. exchanges in the 50 days ended Jan. 18, the fewest since at least 2008, according to data compiled by Bloomberg.

The S&P 500 trades for 13.7 times profits. It was last above the mean valuation since 1954 on May 13, 2010, less than a week after $862 billion was erased from U.S. equity values in 20 minutes, data compiled by Bloomberg show. The slump has surpassed the two longest periods of the last quarter century, in 2008 and 1988.

Profits for the 169 companies in the S&P 500 that reported earnings since Jan. 9 have risen 3.2 percent from a year earlier and beat analyst projections by 2.9 percent, the data show. Apple Inc. in Cupertino, California, the world's biggest technology company, Providence, R.I.-based defense contractor Textron Inc. and 110 other companies posted higher- than-forecast earnings in the three months ending Dec. 31.

Big Surge

Companies in the S&P 500 earned $657 billion in the first nine months of 2011, including $225.2 billion between April and June, the most for any quarter in at least 12 years. That's 72 percent more than the comparable period in 2008. U.S. GDP, which grew at a slower-than-forecast 2.8 percent rate in the fourth quarter, totals about $13.4 trillion, data compiled by Bloomberg and the Commerce Department show.

"Corporate America is extremely lean, extremely efficient at this time," said Peter Sorrentino, a senior fund manager who helps oversee $14.5 billion at Huntington Asset Advisors in Cincinnati. "You can accumulate these stocks at attractive valuations."