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Understanding Standard Deviation in Investing


Standard deviation is a fundamental concept in investing, serving as a key measure of volatility and risk. By understanding standard deviation, investors can gauge the variability of investment returns relative to their average return.

What is Standard Deviation?

Standard deviation quantifies the degree of variation or dispersion of a set of values. In investing, it measures how much an investment's returns can deviate from the average return, providing insights into its volatility and inherent risk.

Importance of Standard Deviation in Investing

The significance of standard deviation lies in its ability to measure investment risk. A smaller standard deviation indicates less volatility, making an investment more predictable. Conversely, a larger standard deviation suggests higher dispersion of returns and greater risk.

Calculating Standard Deviation

The calculation of standard deviation involves several steps: 1. Determine the mean (average) return of the investment. 2. Calculate the variance for each period by subtracting the mean from the actual return, squaring the result, and then averaging these squared differences. 3. The standard deviation is the square root of this variance.

Practical Example

Consider two stocks, XYZ and ABC, each with an average annual return of 10% over ten years. XYZ exhibits higher year-to-year variation in returns compared to ABC, which has more consistent returns around the 10% average. This implies that XYZ has a higher standard deviation, indicating more volatility and risk than ABC.

Standard Deviation and Investment Risk

Standard deviation provides a statistical basis for assessing investment risk. Investments with a wide range of returns are deemed riskier. The principle of normal distribution underlies this, where most values fall within one standard deviation of the mean 68% of the time.

Standard Deviation vs. Variance

It's important to differentiate between standard deviation and variance. While both measure risk and volatility, standard deviation is the square root of variance and is generally easier to interpret since it is in the same units as the original data.


Understanding standard deviation is crucial for investors to assess the risk and volatility of their investments. It provides a quantitative measure to compare the risk levels of different investment options, aiding in making informed decisions.