Standard Deviation
Square root of the variance — measure of dispersion in the original units of the data.
Also known as: std dev, stdev, SD, σ, s
The standard deviation (or for the population) is the square root of the variance. It is expressed in the same units as the data and can be interpreted directly — e.g. "±0.03 mm average deviation from the target".
For approximately normal data, about 68 % of values fall within ±1 s of the mean, 95 % within ±2 s and 99.7 % within ±3 s — the so-called 68-95-99.7 rule that underpins the 6-σ definition.
See also
Used in
- Histogram
- Boxplot
- Process Capability
- Hypothesis Test
- Regression Analysis
- Regression (Attributive)
- Correlation Analysis
- MSA Type 2
- DoE Planner
- DoE Advisor
- Sample Size
- Data Transformation
- Distribution Fit
- Calculator
- Outlier Test
- Multivariate Control Chart (Hotelling T²)
- Pairwise Comparison
- Control Chart
- Individual Value Plot
- XY Plot
- Probability Plot
- Run Chart
- Control Chart (Short-Run Z-MR)
- Control Chart (Attribute)
- Control Chart (Time-Weighted)
- Control Chart (Box-Cox transformed)
- MSA Type 1
- Random Generator
- Data Collection
- Response Optimization
In the Algorithm Lab
Sources
- Montgomery, D.C.: Introduction to Statistical Quality Control, 8th ed., Wiley, 2020
- AIAG: Statistical Process Control (SPC) Reference Manual, 2nd ed., 2005