When you are comparing two distributions, the more different they are, the less samples you need to find out they are different. So the answer to "how many trades" questions is "it depends". You can compare at any time, with any number of trades, and find a % chance that the two distributions are different. The book where I got this from is by Box, Box, and Hunter, called "Statistics for Experimenters". If you have a really strong edge, it won't take long to find out when it dissapears. If the trade methodology isn't much better than random to begin with, it will take a large number of trades. Anyway, it's a suprisingly simple process once you write/obtain that monte carlo program. And the program is not too hard to write either. As for my personal situation, I only have 18 trades so far over the course of 3 months, and everything looks peachy so far. In all my previous 2 yrs trading I didn't have a rock solid methodology like I do now, so in that way i'm a complete newbie. I think the best thing I learned is this: you don't have to lose very much at all to find out when that edge starts to deteriorate. In some cases you might still be making a little money.