“We just have to respect the uniformity of the market’s action,” Ramsey said in a July 16 phone interview. “Until it gets more disjointed, the odds are for even higher highs.”

The S&P 500’s rally from January to June was the best first half since 1998. A total of 460 stocks in the index are up this year, the most since at least 1990, and more than 90 percent traded above their 200-day rolling averages last week, data compiled by Bloomberg show. That compares with 62 percent over the past 23 years.

That’s a reason for caution, said Leo Grohowski, chief investment officer of New York-based BNY Mellon Wealth Management, which oversees $188 billion. Increases in stock market breadth will work against bulls should earnings growth slow and investors become convinced all at once that Bernanke will curtail stimulus as the economy improves.

Profit Growth

“I would be careful about assuming the past as a reliable indicator for the future mainly because the interest rate support for the market is not going to be as strong,” he said in a July 17 telephone interview. “Actual news of economic improvement will increase concern about the Fed removing the punchbowl of liquidity.”

Reports showing U.S. economic growth is picking up while it slows elsewhere have given American equities the third-best returns in the developed world this year, behind Japan and Ireland. American employers added an average of 196,000 jobs in each of the last three months, topping economists’ forecasts. At the same time, China’s gross domestic product grew 7.5 percent in the second quarter from a year earlier and is at risk of the weakest expansion in 23 years.

Profits for the S&P 500 probably rose 2.4 percent in the second quarter from a year ago, according to more than 11,000 analyst estimates compiled by Bloomberg. That compares with an average of 4.3 percent in the last five earnings periods and 28 percent in 2010 and 2011. About 73 percent of companies have exceeded forecasts this month, matching last quarter.

Equity Valuation

Average U.S. price-earnings ratios have expanded by 15 percent this year. At 16.3, the S&P 500 multiple is near the highest since the middle of 2010 and compares to 17.5 when the last bull market ended in October 2007.

The simultaneous rallies are “coincidence” and valuations suggest past patterns are unlikely to be repeated, Uri Landesman, president of New York-based hedge fund Platinum Partners, who helps manage about $1.2 billion, said by phone July 18. “The market is priced for perfection and there is hardly perfection in the world,” he said.