Standard Deviation Calculator — 公式
## How to Calculate Standard Deviation
### Formula
**Population SD (sigma) = sqrt( Sum of (xi - mean)^2 / N )**
**Sample SD (s) = sqrt( Sum of (xi - mean)^2 / (n - 1) )**
Standard deviation is the square root of the variance and is expressed in the same units as the original data. About 68% of data in a normal distribution falls within one standard deviation of the mean.
### Formula
**Population SD (sigma) = sqrt( Sum of (xi - mean)^2 / N )**
**Sample SD (s) = sqrt( Sum of (xi - mean)^2 / (n - 1) )**
Standard deviation is the square root of the variance and is expressed in the same units as the original data. About 68% of data in a normal distribution falls within one standard deviation of the mean.
计算示例
Find the standard deviation of 4, 8, 6, 5, 7.
- Mean = 30 / 5 = 6
- Squared deviations: 4, 4, 0, 1, 1
- Sum of squares = 10
- Sample SD = sqrt(10 / 4) = sqrt(2.5) ≈ 1.5811
- Population SD = sqrt(10 / 5) = sqrt(2) ≈ 1.4142