(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.

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