1. Definition
For sample data, mean x̄=Σx/n and sample variance s²=Σ(x−x̄)²/(n−1) (unbiased), with SD s.
2. Formula & Notation
| x̄,s² | Mean, variance |
| n−1 | Degrees of freedom |
3. Properties & Laws
- Sample variance divides n−1 (unbiased);
- Population variance divides n;
- SD is the square root;
- Need at least 2 samples.
4. Steps
- Enter comma-separated data;
- Click "Compute";
- Or click "Load Example".
5. Worked Examples
Example: 2,4,6,8,10: mean 6, variance 10, SD 3.1623.
6. Common Pitfalls
Sample uses n−1;
Population uses n;
Do not mix.