Recently, the CBOE’s Volatility Index ($VIX) has been trading at substantially higher levels than the 20-day historical volatility of the S&P 500 Index ($SPX). While it’s somewhat normal for $VIX to trade higher than historical volatility, the recent differential (over 10 points on some days) has been large enough to raise eyebrows among those who follow these things – e.g., us! In this article, we’ll examine the relationship between $VIX (implied volatility of $SPX options) and historical volatility of the $SPX Index itself.
It is generally accepted that volatility decreases in a bullish market phase and increases during a bearish one. Even on a daily basis, CBOE statistics show that 75% of the time, if $SPX moves one way, $VIX moves the other. When longer periods are considered, the percentage changes (see page two for exact statistics). Yet, recently $VIX has begun to increase even while $SPX is blowing out to the upside. This is unusual action, and we’ll try to examine it in this article.
