Another force in the rebound was buying by quantitative funds such as commodity trading advisers who operating in equity futures, according to a note Friday from strategists at JPMorgan Chase & Co. Those traders, whose selling was blamed for worsening the rout in late August, showed signs of “capitulation” at mid-October and probably amplified the move in equities, strategists including Nikolaos Panigirtzoglou wrote.

“There is still an overhang of short positions in U.S. equity futures, which if unwound could propel U.S. equities even higher from here,” they wrote. “While the position reversal by CTAs points to capitulation by bearish equity investors, the overhang of short positions in US equity futures suggests that there is room for further short covering.”