This chart shows Volatility for Calpine, defined to be the price range as a portion of the average price:
For instance, on 10/19/2005 the average price was 2.38 with a range of 0.11, indicating a Daily Volatility of 4.6%. The Daily Volatility is obtained by dividing the daily range by the daily average. A longer Volatility period such as Weekly Volatility is obtained by dividing the weekly price range by the weekly mean price. This is a different concept from the weekly average of daily volatility.
The red plot shows the actual price. The remaining marks on the plot correspond to the Volatility measured across several time intervals.
According to academic theory, Volatility is exactly equal to Risk. But investors often make a distinction between these two concepts. The different character of Volatility as seen in different time frames, lends some support to the investor's view. During 9 years, the Average Quarterly Volatility of CPN stock price has been 55% while the Average Daily Volatility has been 5%.
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