Backtest Musings
Since my last couple of posts dealt with simple backtesting concepts, I wanted to write today about some potential pitfalls of using backtesting.
When conducting a backtest, always remember that what you’re viewing is “simulated” data. There’s no guarantee that a program executing live will behave exactly the same as it did in a backtest. Unless you’re looking at individual ticks, most backtesting systems will build OHLC bars of the timeframe you give it. The reason why this is important to keep in mind is that this means that you can not determine what the price action looked like mid-bar. This is especially evident on days when major economic numbers come out. Looking at historical data, bars with violent moves simply look like any other bar except with a larger range. Anyone who has traded the US jobs report knows that there’s nothing smooth about it. It only takes one trade to trigger a stop and if it’s a stop market order, there’s no telling where you’ll be filled. If it’s a stop limit order, there’s no telling IF you’ll be filled.
The bottom line is that there is no substitute for testing with live data and if your results look too good to be true, they probably are. Always be mindful of outlying days and try to figure out a reason for the abnormal results.
Above all, remember that computers make great tools and as much as it may seem otherwise, they are ultimately stupid. This means that for any system, it is only capable of performing as instructed.
Until the next time, Happy Trading and good luck!








