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 3/18/2010 of 1.9%, the price range for the day (0.38) was divided by the average price (19.88). Daily Volatility (the daily range as a portion of the daily average price) is plotted in green. Blue is Weekly Volatility, which is the weekly range as a portion of the weekly average price. This is a different concept from the weekly average of daily volatility.
For reference, the price is plotted in red. Volatility, as measured through various intervals, ( Daily, Weekly, Monthly and Quarterly) is plotted according to color.
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 21 years, the Average Quarterly Volatility of EAT stock price has been 28% while the Average Daily Volatility has been 3%.
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