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Volatility is defined as the price range for a period, divided by the average price for the period: So, to derive the Daily Volatility on 1/28/2011 of 1.9%, the price range for the day (0.48) was divided by the average price (25.25). 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. For reference, the price is plotted in red. The remaining marks on the plot correspond to the Volatility measured across several time intervals. Investors often make a distinction between the concept of Volatility, and the concept of Risk. Academics define them to be exactly equivalent, but as can be seen here, there is good reason to distinguish between the levels of volatility or risk experienced across different time frames. During 29 years, the Average Quarterly Volatility of VLO stock price has been 33% while the Average Daily Volatility has been 3%. |
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If you have ever seen a "yield curve" you should be able to understand the concept behind this "yield curve". These Volatility Curves each apply to a discrete time interval. From left to right, each position plots the Volatility associated with increasing intervals of time. However, as seen in this plot of the VLO Volatility Curve, the increase is not constant. |
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A frequency distribution of the green points on the first chart (the daily volatility) yields this histogram. |
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In a similar vein, the Frequency Distribution of the Quarterly Volatility is plotted here. This is the distribution of the values plotted in purple on the top chart from this page. |
Refined Volatility Risk Analysis for VLO : |
| Friday, February 18, 2011: We have news on Fiserv, Inc., ticker symbol FISV. Signs of an over-bought condition have become noticable. Also, there are breaking events concerning Zimmer Holdings, Inc. and D.R. Horton, Inc.. From the News Archive: (2/18/2011 ) Favorable events happened at Robert Half International Inc. and Southwestern Energy Company. Meanwhile, bad news came from McCormick & Company, Incorporated and Reynolds American, Inc.. |