Analysing monthly forex trading performance in changing market conditions

In my previous post, I discussed about 3 reasons why I don’t use Jensen’s alpha or Sharpe ratio for my montly trading performance measurement.  In this post, I will talk about what I actually use and how I came up with it.

As I was saying in the previous post, what one chooses to use as their performance metric depend on 3 factors such as your style of trading, your agenda, and your interest in this topic.  I will briefly lay out my 3 motives as background information.

I use a swing trading strategy for trading forex.  I aim to hold for at least a few hours to a few days. I am working to hold longer and trade less in the future, but that’s another story.  To fit my style of trading, a performance metric has to be unbiased for long and short trades as well as taking into account short term conditions in the market.

In terms of agenda, what is the purpose of my performance metric?  As a part-time trader, I answer only to myself.  These numbers are used for my self-improvement and internal month-to-month comparisons only.

Lastly, my interest in this topic of portfolio measurement is limited.  I want something easy to calculate and simple to understand.  I have read a few academic papers on this topic and spent a few hours researching on the web.  That’s about it.

Now that my motives have been laid out, let’s discuss my process for coming up with my trading performance metric.

Ultimately, my assessment on how well I have done for the month is to measure my return based on the risk taken.  In other words,

Performance Metric = Reward / Risk.

My Reward function is simple.  I just steal the idea from Sharpe and use:

Reward = Net Return – Riskless Return

Shameless.  I know. I don’t want to muck with the Reward function because at the end of the day, it is your account balance that matters.

The Risk function takes some more thought.  On a trade-by-trade basis, the risk taken for a particular trade can be thought of as the stop loss.  It is a amount put at risk to be taken by the market. In other words, risk can be represented by the loss you are willing to take.  On a month-to-month basis, the most important loss value that I pay attention to is my maximum drawdown.  A drawdown imposes a real dent in your account as well as negatively impact your trading psychology.  For these reasons, the maximum drawdown is a variable in my Risk function.

Risk = Max. Drawdown …

However, I am not done yet.  While max. drawdown is important, it is an entirely internal factor.  The risk you take is also affected by the condition of the market.  Using the stop loss analogy again, a 50 pips stop loss can be labelled as both conservative and aggressive risk exposure depending on the volatility of the market in the timeframe you’re trading.  As such, we need to consider volatility in the Risk function.

However, this raises another question, what is volatility.  Long story short, I just snatch the Average True Range (ATR) indicator that I use on my charts in this formula.  However, we can’t just stick a ATR value in because it’s an absolute number.  We need to use a percentage ATR (%ATR) to correspond with all the other percentage numbers in the formula.  And since this is for monthly analysis, I grab the %ATR from a monthly chart.  In particular, I use the monthly %ATR on the U.S. dollar futures chart.

Finally, the Risk function is:

Risk = Maximum Drawdown + %ATR

Thus,

Performance Metric = (Net Return – Riskless Return) / (Maximum Drawdown + %ATR)

As an example, here are the values I plug in for each variable to calculate my performance metric for November.

Net Return = 3.15%, read from November’s statement

Riskless Return = 0.54% (per annum) / 12 = 0.045%.  This is the Canadian 1-year treasury rate in November.

Max. Drawdown = 3.55%, read from November’s statement

%ATR = monthly ATR(3) of U.S. dollar futures / monthly close of U.S. dollar futures = 3.1473/74.895.

To verify the efficacy of this performance metric.  Let’s do a mental check of my criteria as discussed.

1. Unbiased for long and short trades? Yes, it uses the net return regardless of which side you took.
2. Varies with short term market conditions?  Yes, from the %ATR.
3. Comparable between month to month? Yes, the number is normalized by market volatility each month.
4. Easy to calculate?  Yes, it’s can be done in my trade log spreadsheet with a few formulas.
5. Easy to understand? Yes, it’s an interpretation of reward / risk.

As with any other attempt to summarize trading performance into one single value, many assumptions have been taken.  I cherry picked what I needed to assemble a formula.  Some observant reader will notice that this formula is similar to the Sterling and Calmar ratios.
Indeed, this is yet another modified form of these ratios. In fact, I will be referring to this formula as Sterling ratio in my future posts for simplicity.

Related posts:

1. 3 reasons why I don’t use Jensen’s alpha or Sharpe ratio for my forex trading
2. December 2009 Trading Performance Review
3. January 2010 Trading Performance Review
4. October 2009 Trading Performance Review
5. February 2010 Trading Performance Review