How To Calculate Standard Deviation In Python (Setup, Code, Example Analysis)

In the world of trading and finance, understanding statistical measures is crucial for making informed decisions. One such measure that plays a significant role is the standard deviation. It helps investors and traders gauge the volatility and risk associated with a particular asset or investment. 

In this article, we will delve into how to calculate standard deviation in Python, providing you with the tools to analyze and interpret data effectively.

Related reading: – Python strategies for stocks

Understanding Standard Deviation

Before we dive into Python code, let’s briefly review what standard deviation is.

Standard deviation is a statistical measure that quantifies the amount of variation or dispersion in a set of values.

In the context of finance, it is often used to assess the risk or volatility of an investment.

A higher standard deviation indicates greater variability and, consequently, higher risk.

Here is the formula:


  • xi is the value of the i’th point in the dataset
  • x is the mean value of the dataset
  • n is the number of data points in the data set

Python Libraries for Standard Deviation Calculation

Python provides powerful libraries for numerical and statistical operations, making it a preferred choice for data analysis in various fields, including finance. Two commonly used libraries are NumPy and pandas.

In the code below, we import the NumPy library and use the np.std() function to calculate the standard deviation of the given dataset, in this case, a list.


If your data is in a structured format like a DataFrame, pandas provide a convenient method to calculate the standard deviation.

But wait a minute. The data points are exactly the same, yet the standard deviation is not. Why does this happen?

In statistics, the standard deviation is often calculated with Bessel’s correction, which adjusts for the bias in the estimation of the population variance based on a sample.

NumPy’s std function, by default, uses the denominator N – 1 (like the formula above) for normalization. Pandas, on the other hand, use N (population standard deviation) by default. 

To make NumPy and pandas behave consistently, you can use the ddof parameter in both libraries.

Setting ddof=1 in NumPy will make it calculate the sample standard deviation, aligning it with pandas.

And the same can be done with Pandas, which now aligns with the original Numpy calculation.

Calculating The Standard Deviation Manually in Python

The standard deviation can also be calculated manually in Python. Here is the code: 

In this code:

  • Step 1 calculates the mean of the time series.
  • Step 2 computes the squared differences of each data point from the mean.
  • Step 3 finds the mean of these squared differences.
  • Step 4 takes the square root of the mean squared differences to obtain the standard deviation.

This manual approach gives you a basic understanding of the underlying calculations involved in standard deviation.

Keep in mind that using specialized libraries like pandas or NumPy is generally more efficient for larger datasets and is the recommended approach in practical scenarios.

Related readingStandard deviation in trading

Interpreting the Results

Once you’ve calculated the standard deviation, interpreting the result is key.

A higher standard deviation implies greater variability in the data points, indicating a riskier investment.

Conversely, a lower standard deviation suggests less volatility and, potentially, a more stable investment.

Standard deviation is used, for example, when calculating the Sharpe ratio to measure the asset’s returns concerning its volatility.

How to Calculate Standard Deviation In Python – Conclusion

To sum up, calculating standard deviation in Python is a fundamental skill for anyone involved in data analysis, particularly in the fields of finance and trading. Python’s rich ecosystem of libraries, such as NumPy and pandas, simplifies the process, allowing for efficient analysis of market data.

By incorporating standard deviation into your analytical toolkit, you gain a deeper understanding of the risks associated with various investments. This knowledge is invaluable in making well-informed decisions and developing robust trading strategies.


What is standard deviation, and why is it important in trading and finance?

Standard deviation is a statistical measure that quantifies the amount of variation or dispersion in a set of values. In trading and finance, it is crucial for assessing the risk or volatility of an investment. A higher standard deviation indicates greater variability and, consequently, higher risk.

What Python libraries are commonly used for calculating standard deviation?

Two commonly used Python libraries for calculating standard deviation are NumPy and pandas. NumPy provides the np.std() function, while pandas has a convenient method for calculating standard deviation for structured data like DataFrames.

How does NumPy and pandas differ in standard deviation calculation, and why?

NumPy and pandas may produce different standard deviation results due to normalization methods. NumPy, by default, uses Bessel’s correction (N-1) for sample standard deviation, while pandas uses the population standard deviation (N) by default. To align them, you can use the ddof parameter, setting it to 1 for NumPy and leaving it as the default for pandas.

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