Standard Deviation


Standard Deviation is a fundamental concept in statistics and data analysis. It measures the amount of variation or dispersion in a set of data values. In this comprehensive guide, we will explore the essence of Standard Deviation, its relation to Variance, the symbols used to represent it, and provide you with real-world examples, including Python code, to deepen your understanding.

1. What is Standard Deviation?

Standard Deviation, often denoted as σ (sigma) for populations and s for samples, quantifies the degree of spread or dispersion in a dataset. It provides valuable insights into how individual data points deviate from the mean (average) of the data. A high Standard Deviation suggests that data points are spread out widely, while a low Standard Deviation indicates that data points are clustered closely around the mean.

2. Variance

Variance is closely related to Standard Deviation. It is the squared value of the Standard Deviation. In other words, Variance measures the average of the squared differences from the Mean. The formula for Variance is:


  • N is the number of data points.
  • ��Xi​ represents each data point.
  • �ˉXˉ is the mean of the data.

Understanding Variance is crucial as it provides the foundation for calculating Standard Deviation.

3. Standard Deviation

The Standard Deviation is the square root of Variance. It measures dispersion in the same unit as the data itself. The formula for Standard Deviation is:

Standard Deviation(� for populations or s for samples)=VarianceStandard Deviation(σ for populations or s for samples)=Variance​

It is essential to recognize that Standard Deviation provides a more interpretable value compared to Variance, as it is in the same units as the data.

4. Symbols

  • σ (Sigma) is used to represent the population Standard Deviation.
  • s is used to represent the sample Standard Deviation.
  • σ2 (Sigma squared) represents population Variance.
  • s2 represents sample Variance.

Examples with Python Code

Let’s illustrate the concepts of Standard Deviation and Variance with Python:

import numpy as np

data = [12, 15, 18, 21, 24, 27, 30]
mean = np.mean(data)

# Sample Standard Deviation
sample_std = np.std(data, ddof=1)

# Population Standard Deviation
population_std = np.std(data)

# Sample Variance
sample_variance = np.var(data, ddof=1)

# Population Variance
population_variance = np.var(data)

print(f"Sample Standard Deviation: {sample_std:.2f}")
print(f"Population Standard Deviation: {population_std:.2f}")
print(f"Sample Variance: {sample_variance:.2f}")
print(f"Population Variance: {population_variance:.2f}")

In this Python code, we calculate both sample and population Standard Deviation and Variance for a dataset.


In this article, we delved into the world of Standard Deviation, Variance, and the symbols used to represent them. Understanding these concepts is crucial for anyone working with data analysis and statistics. We also provided practical examples using Python, empowering you to apply these concepts in your own data analysis projects. By mastering Standard Deviation and Variance, you’ll become more proficient in interpreting and drawing insights from data, enhancing your skills as a Python programmer and data analyst.