Quote from N54_Fan:
It absolutely is relavant!!! It is MUCH harder to face ruin with 90% win rate than 10%. It all factors together is my point. All of these issues, profit factor, expectancy, and probability of winning trade, and standard deviation between each trade's win and losses also play a role in your overall performance. However, a higher win rate reduces drawdown which HELPS reduce your volatility of your account's equity. The more times your trade is a winner (even if small) will minimize your string of losses and minimize drawdown. With lower probability trades you need bigger profit wins to make up for the multiple losses in a row you would face. I would MUCH rather have a system with 0.3R expectancy and 90% win rate than a 0.4R expectancy and 10% win rate.
Lets say you have a system that has 0.3R expectancy so in 10 trades you have 9 that make on average 0.44R and one 1R loser with total win of 3R in 10 trades = 0.3R Now take a system with 9 losses in a row of 1R each. Your last win would have to be 13R to make up for the 9R losers and make4R divided by 10 trades = 0.4R expectancy in 10 trades. However, because each trade is INDEPENDENT of what occurred on the prior trade it does not matter whether the prior trade won or lost as the prior trade does NOT INFLUENCE the next trade. So your chance of a loss is STILL 90% on the next trade. You easily could rack up 20+ losers in a row with this system and likley only rack up a max of about 2-3 winners in a row. Over 10,000 trades this may all even out but few of us would have the conviction to trade a 90% losing system with HUGE drawdowns of 20 losers in a row or more. Do a Monte Carlo analysis on a system like this and you will see what I mean. This is a poor system to trade...you are better off flipping a coin (50:50) for your trade direction.
This has been explained in GREAT detail in "The Definitive Guide to Position Sizing" by Dr. Van K Tharp for those that are interested in reading more about this.
Again, probability is NOT the end all be all of trading but it sure as hell helps!!!