Math
Standard Deviation Explained
Learn what standard deviation means and how to calculate it.
Measures how spread out data is from the mean.
Why It Matters
Understand reliability, compare datasets, identify outliers.
How to Calculate
- Find mean
- Subtract mean, square each
- Average squared differences
- Square root
Population vs Sample
Population uses N. Sample uses N-1 (Bessel's correction).
68-95-99.7 Rule
Normal: ~68% within 1 SD, ~95% within 2, ~99.7% within 3.
Frequently Asked Questions
Variance vs SD?
Variance = squared differences average. SD = square root, in original units.
Sample vs population?
Population: all data. Sample: subset, use N-1.
High SD meaning?
Data spread far from mean — high variability.