Quick guide
How to use this calculator
- Enter the observations, probabilities, model parameters, or summary statistics requested by the visible labels.
- Keep every value on the same scale and confirm that the selected sampling relationship, distribution, and tail convention match the question you are investigating.
- Read the result together with its assumptions and interpretation. Statistical output summarizes uncertainty under a model; it does not repair biased data or establish causation.
Calculation method
How the pooled standard deviation calculator works
sp = √[Σ(nᵢ−1)sᵢ² / Σ(nᵢ−1)].
Pooled SD estimates common within-group spread; it is not the spread of all observations after groups are merged.
Worked example
Pooled Standard Deviation example
Equal groups with sample SDs 2 and 4 have pooled SD √10, not their arithmetic average of 3.
sp = √[Σ(nᵢ−1)sᵢ² / Σ(nᵢ−1)].
Supported inputs
Precision and limits
Model and design
Pooling is meaningful only when a common within-group variance is a defensible summary; the calculator cannot establish that assumption.
Numerical scope
Inputs use double-precision numerical methods with guarded domains. Datasets accept up to 10,000 finite plain-decimal values. Extremely large parameters or probabilities deep in a numerical tail may require specialist statistical software.
Interpretation
Pooled SD estimates common within-group spread; it is not the spread of all observations after groups are merged.
Decision boundary
The calculator does not validate how data were collected, diagnose dependence or bias, choose a scientifically meaningful effect, or replace review by a qualified statistician for consequential research, medical, regulatory, safety, or policy decisions.
Privacy
Entered values and calculated results stay in this browser and are not sent to an analytics service.
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