The Yen May Be the Best Indicator at Deciphering Yellen's Tone

NEW YORK ( TheStreet) -- As investors await Janet Yellen's comments at the Federal Reserve's annual symposium in Jackson Hole, Wyo., it could be currency fluctuations overseas that tell the most about the future direction of U.S. equities.

Investors are looking to a statement from Yellen, the Fed's chairwoman, for clues about whether the Fed will continue to keep interest rates low as the U.S. economy gradually improves.

Analysts, however, tend to have a difficult time coming to a consensus on whether comments from the Fed lean more dovish or hawkish, unless specific language is used.

Investors may be better suited looking at movements in the U.S. dollar/Japanese yen currency pair following Yellen's comments to gauge the market's reaction.

The U.S. dollar/Japanese yen currency pair, represented by the CurrencyShares Japanese Yen Trust ETF (FXY) , has held a strong negative correlation with SPDR S&P 500 (SPY) during the past five years.

The yen is perceived as a safe-haven currency as it tends to be bid higher during times of economic uncertainty.

Moreover, many investors have difficulty interpreting the price swings in iPath S&P 500 VIX ST Futures ETN (VXX) because it is perceived as a flawed indicator of risk. And so the yen is often seen as a better gauge of global risk sentiment.

As seen in the chart below, periods of big declines in the yen usually set the tone for broader moves higher in U.S. equities.

The yen fell by more than 24% in the final months of 2012 and by more than 7% in 2013. More accommodating monetary policy on behalf of the Bank of Japan was part of the reason, and so was less investor anxiety.

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