What Happen To SPY After Extreme Strong Day

從學習交易以來，我一直把 Dr. Steenbarger 當成是模仿的對象，再來這一系列的文章是以 Dr. Steenbarger <Consecutive Narrow Days: What Comes Nex> 這種文章為範本，來探討 SPY ETF 的特性。

利用 1/2/2002 到 12/18/2009 每日歷史資料 N=2007，我們來看看當 S&P 上漲超過 2.28% 後，再來 1, 3, 5, 10 天的表現。會選擇 2.28% 是因為它剛好是 2 standard deviations from absolute value of daily move，在過去七年來這種情形發生了 50 次：

• Next Day: SPY average -0.01%，20 (40%) down, 29 (58%) up，1 (2%) flat. Down day with average of -1.67, and up day with average of 1.14%.

• 3 Days later: SPY average 0.46%, 21 (42%) down, 29 (58%) up. Down days with average of -3.31%, and up days with average of 3.19%.

• 5 Days later: SPY average -0.4%, 27 (54%) down, 23 (46%) up. Down days with average of -4.2%, and up days with average of 4.06%.

• 10 Days later: SPY average 0.29%, 21 (42%) down, 29 (58%) up. Down days with average of -5.68% and up days with average of 4.27%.

From the first glance, strength seems to have follow through in the immediate three days after the big move, peters out after stretched out to five days, and gaining back strength after ten days.