What is 'Standard Deviation'
Standard deviation is a measure of the dispersion of a set of data from its mean. The more spread apart the data, the higher the deviation. Standard deviation is calculated as the square root of variance.
2. In finance, standard deviation is applied to the annual rate of return of an investment to measure the investment's volatility. Standard deviation is also known as historical volatility and is used by investors as a gauge for the amount of expected volatility.
BREAKING DOWN 'Standard Deviation'
Standard deviation is a statistical measurement that sheds light on historical volatility. For example, a volatile stock will have a high standard deviation while the deviation of a stable blue chip stock will be lower. A large dispersion tells us how much the return on the fund is deviating from the expected normal returns.
Want to know more about risk measurement? Please read Standard Deviation & Value At Risk and The Uses And Limits Of Volatility

Residual Standard Deviation
A statistical term used to describe the standard deviation of ... 
Empirical Rule
A statistical rule stating that for a normal distribution, almost ... 
Downside Deviation
A measure of downside risk that focuses on returns that fall ... 
Historical Volatility  HV
The realized volatility of a financial instrument over a given ... 
Standard Error
The standard deviation of the sampling distribution of a statistic. ... 
Volatility
1. A statistical measure of the dispersion of returns for a given ...

Investing
Standard Deviation
Learn about how standard deviation is applied to the annual rate of return of an investment to measure the its volatility. 
Mutual Funds & ETFs
Standard Deviation
Standard Deviation 
Professionals
Standard Deviation And Variance
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Mutual Funds & ETFs
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Standard Deviation & Value At Risk 
Fundamental Analysis
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The empirical rule provides a quick estimate of the spread of data in a normal statistical distribution. 
Professionals
Confidence Intervals
CFA Level 1  Common Probability Distributions  Confidence Intervals 
Professionals
Stock Risks
NASAA Series 65: Section 16 Stock Risks. In this section types of risks, quantitative analysis and risk measures associated to stock markets. 
Professionals
Expected Return, Variance And Standard Deviation Of A Portfolio
Learn these valuable ways of analyzing your portfolio. 
Forex Education
Trading With Gaussian Models Of Statistics
The entire study of statistics originated from Gauss and allowed us to understand markets, prices and probabilities, among other applications. 
Professionals
Measuring Portfolio Risks
FINRA/NASAA Series 66: Section 5 Measuring Portfolio Risks. This section discusses different risk measures: Beta, Alpha and the Sharpe Ratio.

What does standard deviation measure in a portfolio?
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