If SPY can reclaim the 20-day, then another test of $300 to $302 is in the cards. The 100-day perfectly correlates with the 2018 highs, but marks a big level. Because below this mark, there’s not an immediate level of support in play. $280 has been notable in 2019, but just below near $276 is the 38.2% retracement for the one-year range, with the 200-day moving average at $276.59.
According to one interpretation of the efficient-market hypothesis (EMH), only changes in fundamental factors, such as the outlook for margins, profits or dividends, ought to affect share prices beyond the short term, where random 'noise' in the system may prevail. The 'hard' efficient-market hypothesis does not explain the cause of events such as the crash in 1987, when the Dow Jones Industrial Average plummeted 22.6 percent—the largest-ever one-day fall in the United States.