Bad data making back testing useless?

[alikair]

I witness 2 symbols today drop to the low of the day and back up in a blink of an eye.
There would be no way you could have actually entered a trade if you wanted to.
Not to mention I couldn't even find the trade on the time and sales window.

Yet any back testing program would have said it entered or exited that trade on that day.

My question is, how often does this happen?

I have seen this before but not 2 at the same time. I am worried tradesim may be hitting a bunch of fake trades and calling it good.

My system enters and exits based on support and resistant intra day on a daily chart so there is nothing I can do to avoid this deception.

[David Samborsky]

yes this is a problem because you don't have access to the intraday data to know exactly what went on som some sort of approximation is needed to simulate the history.

having said that I recommend that you stress test your system and simulate it with worst case slippage where you enter at the high of the day and exit at the low of the day or vice versa fro short trades. This can easily be done in TradeSim in the Trade Preferences tab where you select worst case slippage for entry and exit.

[alikair]

Thanks David.

I think I tried that before and my profits dropped an incredible amount.

I am more interested in knowing how often this happens where the simulator takes a trade that in real life was impossible to do.