If we take a scalping system that makes a mean of 20 pips on a profitable trade and loses a median thirty pips on a loss-making trade, with 80% of its trades being profitable and only twenty percent losses, this is the edge for this system:
Edge = (80% x 20 pips) – (20% x 30 pips) = 10 pips
That would be a profitable system and a very good one to use if you had an interest in changing into a scalper. However, you might find a very different sort of system that had results that were just as good. For instance, you could come across a system that worked the opposite way, with lots of small losses, say 60% losses of ten pips everytime, and then some bigger gains, making say forty pips average profit on successful trades. For this system,
Edge = (40% x 40) – (60% x 10) = 10 pips
So these two completely different systems have precisely the same results, and the choice on which was the best foreign exchange trading system for you would be wholly conditional upon your trading style. A good way to check this out is usually to operate both systems in a demo account, say for one month each. At the end of the month you could analyze the unproven results from a back test over the month to see how your own results varied from the back tests. This could be a handy comparison when picking the best forex trading system from numerous systems that are rewarding in theory.