Sunday, May 20, 2018

Backtesting 1987

You would want to make sure that your trading model put you in the right direction in the 1987 crash (which I am old enough to remember very well), wouldn't you? So, I backtested the model for 1986-87. The main model would be short going into the crash. But a more primitive model I am using in conjunction with the main model would switch to long on the Friday before the crash. That day the market went down 5%, so it would have already been a bad idea on the Friday. Recently, this secondary model has been doing well and I have combined its signals with my main model. So, we need some new rules about how and why to combine them. In this chart you can see that the buy signal would have come with the price already outside the +/- 2 standard deviations envelope (S&P 500 index):

These are "Bollinger Bands", though I use a 34 day moving average instead of Bollinger's 20 day MA. So, the new rule is not to take that signal when the price is outside the Bollinger Bands and the width of the Bollinger Bands is increasing. That wouldn't change much recently (NASDAQ 100 index):

The secondary model gave some very good buy signals just as price hit the Bollinger Bands in early February and late March. In these cases the price was not outside the Bollinger Bands or they weren't expanding.

The model is short for Monday.

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