Originally posted by Jim Bartley
There is guy by the name of John Sweeney who used to write for "Technical Analysis of Stocks & Commodities" magazine. He wrote a book about something called Maximum Adverse Excursion(MAE....Then you list these in the manner of a bell curve or other graphic representation. ....
I would like to add some comments on that technique. In the graph below, I took the trades from a backtest and plotted P/L vs MAE, where MAE was plotted as
MAE if P/L > 0 and
-MAE if P/L < 0 (MAE usually is stated as a positive number),
to fit a straight line to the MAE. In fact you should plot P/L vs MAE for long and short trades seperately.
You may use this plot to search for cut-off points, i.e. ask yourself: if I stop these trades here, how many trades will turn into losers.
The most important point then is to rerun your backtests with a stop set to the cut-off point you found this way (difficult, when you trade by discretion). To not do this is a severe mistake and I have seen articles on MAE where this step has not been performed (e.g. "Setting Stops and Taking Profits with Maximum Excursion" in TASC August 2002).
Why is rerunning your tests important? Because when you cut-off your trades you exit them usually earlier than when not cutting-off and this influences all subsequent trades: you get different conditions for entry (and exit). The effect is then that you may get a different number of trades with different results from your previous test.
The authors that do not rerun their tests usually have a list of their trades in Excel and just look at each trade what would have happened if it had been stopped at the cut-off point. Their results usually are too positive.
In my experience (only a limited number of tests, but the other people did even test less) using MAE will lower your profits and hoepfully reduce your drawdown even more, i.e. the volatility of your equity might be reduced.
Some trading systems do not react well to this technique, especially those using NNs. I suspect they have been curve-fitted a lot.
Regards
Bernd Kuerbs