midProbability
What is variance and standard deviation?
Updated May 17, 2026
Short answer
Variance measures spread of data; standard deviation is its square root.
Deep explanation
Variance is E[(X - μ)^2], capturing dispersion around the mean. Standard deviation provides the same measure in original units, making it more interpretable.
Real-world example
Risk measurement in stock price fluctuations.
Common mistakes
- Confusing variance units with original data units.
Follow-up questions
- Why square deviations?
- What is high variance?