To be an effective trader, understanding your overall portfolio's sensitivity to market volatility is important. But this is particularly so when trading forex. Because currencies are priced in pairs, no single pair trades completely independently of the others. Once you know about these correlations and how they change, you can take advantage of them to control over your portfolio's exposure.
Defining Correlation The reason for the interdependence of currency pairs is easy to see: if you were trading the British pound against the Japanese yen (GBP/JPY pair), for example, you are actually trading a kind of derivative of the GBP/USD and USD/JPY pairs; therefore, GBP/JPY must be somewhat correlated to one if not both of these other currency pairs.
However, the interdependence among currencies stems from more than the simple fact that they are in pairs. While some currency pairs will move in tandem, other currency pairs may move in opposite directions, which is in essence the result of more complex forces. Correlation, in the financial world, is the statistical measure of the relationship between two securities. The
correlation coefficient ranges between -1 and +1. A correlation of +1 implies that the two currency pairs will move in the same direction 100% of the time. A correlation of -1 implies the two currency pairs will move in the opposite direction 100% of the time. A correlation of zero implies that the relationship between the currency pairs is completely random.
Reading The Correlation Table With this knowledge of correlations in mind, let's look at the following tables, each showing correlations between the major currency pairs for the month of March 2005.
The upper table above shows that over the month of March (one month) EUR/USD and AUD/USD had very strong positive correlation of 0.94. This implies that when the EUR/USD rallies, the AUD/USD will also rally 94% of the time. Over the longer term (three months), though, the correlation is slightly weaker (0.47).
By contrast, the EUR/USD and USD/CHF had a near-perfect negative correlation of -0.99. This implies that 99% of the time, when the EUR/USD rallies, USD/CHF will undergo a selloff. This relationship even holds true over longer periods as the correlation figures remain relatively stable.
Yet correlations do not always remain stable. Take USD/CAD and NZD/USD, for example. With a coefficient of -0.94, they had a strong negative correlation over the past year, but the relationship deteriorated over March 2005 for a number of factors, including the Reserve Bank of New Zealand's intentions to resume rate hikes, and political instability in Canada.
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