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How to calculate average drawdown of a trading system?
First of all, I think I'll clear off some confusion in the topic. The Sterling Ratio is a very simple investment portfolio measurement that fits nicely to the topic of personal finance, although not so much to a foreign exchange trading system. The Sterling Ratio is mainly used in the context of hedge funds to measure its risk-reward ratio for long term investments. To do so, it has been adapted to the following in order to appear more like the Sharpe Ratio:  I Suppose this is why you question the Average Largest Draw-down. I'll come back to that later. It's original definition, suggested by the company Deane Sterling Jones, is a little different and perhaps the one you should use if you want to measure your trading system's long term risk-reward ratio, which is as followed:  Note: Average Annual Draw-down has to be negative on the above-mentioned formula. This one is very simple to calculate and the one to use if you want to measure any portfolio's long-term results, such an example of a 5 or 10 years period and calculate the average of each years largest drawdown. To answer @Dheer's comment, this specific measurement can also be used in personal investments portfolio, which is considered a topic related to personal finance. Back to the first one, which answers your question. It's used in most cases in investment strategies, such as hedging, not trading systems. By hedging I mean that in these cases long term investments are made in anti-correlated securities to obtain a diversified portfolio with a very stable growth. This one is calculated normally annually because you rely on the Annual Risk-Free Rate. Having that in mind I think you can guess that the Average Largest Drawdown is the average between the Largest/Maximum Drawdown from each security in the portfolio. And this doesn't make sense in a trading system. Example: If you have invested in 5 different securities where we calculated the Largest Draw-down for each, such as represented in the following array: MaxDD[5] = { 0.12, 0.23, 0.06, 0.36, 0.09 }, in this case your Average Largest Draw-down is the average(MaxDD) that equals 0.172 or 17,2% If your portfolio's annual return is 15% and the Risk-free Rate is 10%, your Sterling Ratio SR = (0.15 - 0.10)/0.172, which result to 0.29. The higher the rate better is the risk-reward ratio of your portfolio. I suggest in your case to only use the original Sterling Ratio to calculate your long-term risk-reward, in any other case I suggest looking at the Sharpe and Sortino ratios instead.