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September 11th, 2001 was a fateful, horrific day in the U.S. (and global) history. As always, on this day we remember the events and the toll taken.

How has the stock market reacted in and around the anniversary of September 11 over the past 10+ years?

We looked at the S&P 500 Index [SPX] (SPY) on the day preceding, the day of, one day after and five trading days after - using SPX closing data since 2002. If September 11 fell on a weekend, we used the next trading day.

This was done to see what kind of jitters or directional bias, if any, the market had around these dates, and if volatility (from news events or just internal) seemed to increase.

Here are the summarized results:

SPX Performance Table
(click to enlarge)

Three things jump out from the data above, which is a sample size of 11 years:

  • The day of September 11th, the market has ended higher 8/11 times (73%) compared to the previous close, however the size of the moves have tended to be fairly small (only three moves over 1% plus/minus).
  • The day following September 11, the market has again ended higher 8/11 times (73%) compared to the September 11 close. Again here the size of the net moves hasn't been large in general (only two moves greater than +/- 1%).
  • In the five trading days following September 11, the market has shown a propensity for a more sizable move. The net gain/loss has been over 1.5% 9/11 (82%) times in that time, with seven (64%) of the occurrences being bullish.

So based on the data since 2002, there has tended to be a bullish bias around market performance on September 11, the trading day following and the five trading days (or roughly a week) following. Also a stronger tendency for net market trend movement volatility over the five trading days.

Source: Stock Market Performance Around September 11th Since 2002