ETF Pairs as Sentiment Gauges: SPY and VXX

Heres a chart of the SPY (S&P 500 ETF) vs the VXX ( Volatility Index ETF or VIX ETF). It is clear that when ever the SPY goes up the VXX goes down and vise versa. Theres an -87% correlation between the two always confirm each other and reflect market sentiment. When the VXX is above the SPY the market is bearish and when the SPY is above the VXX the market is bullish.