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obitools4/autodoc/docmd/pkg/obistats/ttest.md
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Eric Coissac 8c7017a99d ⬆️ version bump to v4.5
- Update obioptions.Version from "Release 4.4.29" to "/v/ Release v5"
- Update version.txt from 4.29 → .30
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# Statistical Hypothesis Testing Module (`obistats`)
This Go package provides implementations of common **t-tests** for comparing sample means under different assumptions. It supports one- and two-sample tests, paired or unpaired designs.
## Core Types
- **`TTestResult`**: Encapsulates the outcome of a t-test, including:
- Sample sizes (`N1`, `N2`)
- Test statistic value (`T`)
- Degrees of freedom (`DoF`)
- Alternative hypothesis type (`AltHypothesis`: `LocationDiffers`, `LocationLess`, or `LocationGreater`)
- Computed *p*-value (`P`)
- **`TTestSample` interface**: Requires methods `Weight()`, `Mean()`, and `Variance()` — enabling reuse with summary statistics.
## Supported Tests
1. **`TwoSampleTTest(x1, x2)`**
Standard Students *t*-test for two independent samples assuming **equal variances** and normality.
2. **`TwoSampleWelchTTest(x1, x2)`**
Welchs *t*-test for two independent samples **without equal-variance assumption**, using Satterthwaite approximation for degrees of freedom.
3. **`PairedTTest(x1, x2)`**
Paired *t*-test for dependent samples (e.g., before/after), testing mean of differences against `μ0`.
4. **`OneSampleTTest(x)`**
One-sample *t*-test comparing sample mean to a known population mean `μ0`.
## Error Handling
- Returns errors for invalid inputs: zero sample size (`ErrSampleSize`), zero variance (`ErrZeroVariance`), or mismatched paired sample lengths (`ErrMismatchedSamples`).
## Implementation Notes
- *p*-values are computed using the cumulative distribution function (CDF) of the Students *t*-distribution.
- Designed for statistical rigor and modularity, reusing internal utilities (e.g., `Mean`, `StdDev`) from a shared module.