Originally posted by NASCARFan
100 share lots barely keep you above the fees, but I am sure you knew that already. To make a living off ANY day trading system, one needs to trade in larger lots sizes.
See if
www.interactivebrokers.com can change that opinion of yours.
One more thing:
I once developed an extremely profitable daytrading system. I found a setup that was profitable for certain values of its parameters, set the parameters accordingly, optimized it a little bit, and let my computer apply it to the last 100 trading days. It did 700 trades and made a little more than 100%, always trading only 100 shares at a time.
Next, I calculated the probability that my system was NOT consistently profitable and the results I was seeing were pure coincidence. That probability was something in the vicinity of .5%. That meant that I could be 99.5% sure that my system actually had a positive expectancy.
I started trading the system in real time (fortunately I decided to still paper trade for a week or two, just to be sure), and it lost money the first day. It lost again on the second day. To cut a long story short, it became more and more obvious that my system indeed had an expectancy just around zero.
So I developed a completely different daytrading system in much the same way (by finding parameters for which it backtested profitably), let it run through a few hundred trades, determined that there was a 99.some odd % chance that it would be consistently profitable, and it turned out to only break even in real time paper trading. Just like the first one.
Note that slippage is NOT the reason for this phenomenon, since I never actually traded real money, so any miscalculation of slippage would be IN ADDITION to the effects observed.
If you can explain to me exactly how on earth it is possible that each one of those systems has such a miniscule probability of failure, yet each and every one DOES fail in real time tests, then we can start talking business.
To all others: I know the answer to my question is easy, albeit not trivial, and I am sure some of you know it, but please don't spoil it for NASCARFan!