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# Understanding the Four Measures of Volatility

Updated from 3/8/2007 at 2:15 p.m. EST

"Volatility" is a term that is increasingly interjected into financial market commentary by the press and professionals. In fact, Bloomberg Radio has a daily "Volatility Report." While the term is being thrown around with a seemingly high degree of expertise, I find that the concept is not well understood by most commentators and the average investor. This module of TheStreet University will cover the four main types of volatility measures:

• historical volatility;
• implied volatility;
• the volatility index; and

Type 1: Historical Volatility

Volatility in its most basic form represents daily changes in stock prices. We call this historical volatility (or historic volatility) and it is the starting point for understanding volatility in the greater sense. Historic volatility is the standard deviation of the change in price of a stock or other financial instrument relative to its historic price over a period of time. That sounds quite eloquent but for the average investor who does not command an intimate knowledge of statistics, the definition is most overwhelming.

Think of a Pendulum

To help you visualize the concept of volatility, think of a pendulum like in the picture below. The pendulum is constructed from a steel ball, attached to a rope and then suspended from a ceiling.

The pendulum starts at the resting state when our ball is at point 2 (the mean). If you raise the ball to point 1 and let it go, the ball would then swing from point 1 to point 3. Over time that ball will swing back and forth always passing though point 2. If this were a stock, the difference in distance from point 1 to point 2 or from point 2 to point 3 represents the volatility in the movement of the stock price.

So as not to get into any trouble with physicists out there, the formulas for standard deviation and movement of a pendulum are different and I am not equating the two from a statistical perspective. Rather, I am only using the pendulum as a visual aide. Stocks with a swing that is greater from point 1 to point 2 vs. that of another stock will have a higher volatility than the other stock.

Now imagine a wind hitting the metal ball. The force of that wind will increase a stock's volatility. Market corrections, increases in uncertainty or other causal factors of risk will be the wind that shifts volatility higher. Say that there is no wind, but rather calm over the markets. Since there is no outside force to apply motion to the pendulum, the arc of the movement from point 1 to point 3 will decrease. This is when volatility declines. Some call this complacency, but it is generally viewed as a market with low or declining volatility.

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