Low volatility is past perfect

Three main subjects in this article: some explanations on historic stock market volatility and how it is derived, an overview of rallies and swoons both in the 21st and the 20th century and finally a discussion on the trend of volatility since the start of the 21st century.

Vigorous short-lived bear market bounces

There is nothing as vigorous as a bear market rally. After a severe swoon, the market gets oversold. Earlier sellers see an opportunity to get back in much cheaper, while cautious shorts may want to cover and lock in decent gains. When this mindset gets root among investors and speculators, a bear market rally is born. However, there is nothing as short-lived as a bear market rally. That's why I called them “bear market bounces” in the blog title.

Volatility persists

Historic volatility is calculated using a time series of index (or stock price) close values. It is defined as the standard deviation on the series of percentage day-to-day variations. When considering all day-to-day variations, we obtain one single historic volatility, which - while illustrative - raises a mainly academic interest.