(Bloomberg) — The single-session equity rout that wiped $500 billion from U.S. stocks Friday served up a technical signal that bodes well for bulls betting shares will close higher this year.

The S&P 500 Index's 2.5% selloff left 52% of its members at a 20-day low, Strategas Research Partners found. In prior times when half or more of the benchmark for American equity slid below that threshold, the index has seen an average increase of 4.4% over the following 65 days, the firm's research shows. The S&P 500 rebounded Monday 1.5% to 2,159.04, the biggest reversal since January.

Friday's rout broke eight weeks of calm on global financial markets as concern mounted that central banks are growing skeptical additional stimulus will work. Selling that spread to all corners of the financial markets was undone Monday as investors piled into equities that bore the brunt of the worst decline for U.S. stocks since Britain voted to secede from the European Union.

"A fair amount of the latter part of Friday was emotional selling, and emotional trading tends to have a short lifespan," said Michael James, managing director of equity trading at Wedbush Securities in Los Angeles. "Traders were a little more willing to put some risk back on the long side."

The S&P 500 rallied back into a trading range it had held since mid-July, with Friday's biggest losers leading gains. Phone and utility shares jumped more than 1.7%, following routs that were the worst since at least February 2015. For Chris Verrone, partner and head of technical analysis at New York-based Strategas, the dip was an opportunity to buy because U.S. shares remain in an upward trend, a technical measure the firm calculates by plotting stocks against moving averages, among other things.

"We are more inclined to view weakness as buyable with another run at new highs likely into year-end," Verrone wrote in note to clients on Monday. That would push the S&P 500 above 2,190, implying a gain of almost 3% from Friday's close.

The technical bullishness conflicts with the views of Wall Street equity strategists, who see the S&P 500 slipping from its current level to end the year at 2,156, according to estimates compiled by Bloomberg. The biggest bear, Ben Laidler of HSBC Holdings, foresees the benchmark losing more than 9% to 1,960 by year-end.

The last time more than half the S&P 500 members fell to a 20-day low was June 27, after the Brexit referendum sparked a 5.3% rout over two days. The index rallied 8.2% in the next 12 days. Before that, the threshold was breached in January during the worst-ever start to a year. Equities bottomed Feb. 11 and surged 15% by April 20.

Technical analysts from BTIG and MKM Partners also saw little chance for a prolonged downturn headed into Monday's trading, though both predicted additional selling in the short-term.

MKM's Jonathan Krinsky said that 71% of S&P 500 members ended Friday above their average price for the past 200 days, a signal that any downturn would be short-lived. "We still think bulls win the game," he wrote in a note to clients.

"Our short-term indicators are supportive of additional downside, but we think the pullback will mature quickly and will be looking for signs of downside exhaustion," BTIG's Katie Stockton wrote.

Extreme pessimism in the stock market has pushed a measure of positioning for speculative ETF investors so low that it would now be prudent to buy, Tony Welch, ETF strategist at Venice, Florida-based Ned Davis Research, wrote in a client note on Monday.

"The speculative crowd has increased their bearish bets to a point that our indicator is nearing a new, pessimistic buy signal," Welch wrote. The past 17 instances of such a signal resulted in the S&P 500 rising 1.8% on average a week later and 4.5% after four weeks, the firm's data going back to 2007 show.

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