What is 'TimeVarying Volatility'
Timevarying volatility refers to the fluctuations in volatility over different time periods. Investors may choose to study or consider volatility of an underlying security during various time periods. The use of timevaried volatility measures can influence the expectations of investments.
BREAKING DOWN 'TimeVarying Volatility'
Timevarying volatility can be studied in any timeframe. Generally, volatility analysis requires mathematical modeling to generate volatility levels as one measure of the risk of an underlying security. This type of modeling generates historical volatility statistics.
Historical volatility is generally referred to as the standard deviation of prices for a financial instrument, and hence a measure of its risk. Over time a security is expected to have varying volatility subject to large swings in price, with stocks and other financial instruments exhibiting periods of high volatility and low volatility at various points in time.
Analysts may also use mathematic calculations to generate implied volatility. Implied volatility differs from historical volatility in that it is not based on historical data but rather a mathematical calculation that provides a measure of the market’s estimated volatility based on current market factors.
Historical Volatility
Historical volatility can be analyzed by time periods based on the availability of data. Many analysts seek to first model volatility with as much available data as possible in order to find the volatility of security over its entire life. In this type of analysis, volatility is simply the standard deviation of a security’s price around its mean.
Analyzing volatility by specified time periods can be helpful for understating how a security has behaved during certain market cycles, crises or targeted events. Time series volatility can also be helpful in analyzing the volatility of a security in recent months or quarters versus longer timeframes.
Historical volatility can also be a variable in different market pricing and quantitative models. For example, the BlackScholes Option Pricing Model requires the historical volatility of a security when seeking to identify its option price.
Implied Volatility
Volatility can also be extracted from a model such as Black Scholes to identify the market’s current assumed volatility. Generally implied volatility’s timeframe is based on the time to expiration. Overall, options with a longer time to expiration will have a higher volatility while options expiring in a shorter amount of time will have a lower implied volatility.
2003 Nobel Prize
In 2003 economists Robert F. Engle and Clive Granger won the Nobel Memorial Prize in Economics for their work in studying timevarying volatility. The economists developed the Autoregressive Conditional Heteroskedasticity (ARCH) model. This model provides insight for analyzing and explaining volatility over different time periods. Its results can then be used in predictive risk management which can help to mitigate losses in a variety of different scenarios.

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