---
title: "Bland-Altman method-agreement analysis"
method_id: SM.RLB.AGR.METH.BLANDALT
family: Reliability
version: 1.1.0
date_modified: 2026-06-18
canonical: https://clarus.ofrencber.com/library/bland_altman.md
source: Clarus method library
---

# Bland-Altman method-agreement analysis

> A classical statistical method in the Clarus library (Reliability family).
> Clarus selects, assumption-checks and runs this method on your data with a
> deterministic rule engine and real numerical libraries (scipy / statsmodels);
> it never generates numbers, citations or results.

**Also known as:** Bland-Altman plot; limits of agreement analysis; Tukey mean-difference plot.

## Hypotheses

- **Null (H0):** not_applicable
- **Alternative (H1):** not_applicable

## When to use it

Use this method when your goal is to:
- assess agreement between two measurement methods
- method comparison
- quantify measurement bias and limits

## Data it expects

- **dependent:** 2 continuous measurements of the same quantity
- **independent:** none
- **pairing:** paired (same subject measured by both methods/instruments/raters)

## Assumptions Clarus checks

- **differences normality** (gate: shapiro_wilk; severity: warning; on violation: warn_only)
- **bias independent of magnitude** (severity: warning; on violation: warn_only)
- **constant variability** (severity: warning; on violation: warn_only)

## Effect size reported

- **limits of agreement** (Bland & Altman (1986))

## Honest limitations

- A high correlation between the two methods does NOT imply agreement — correlation can be near 1 even with large systematic bias. Use the bias and limits of agreement, not r.
- Whether the limits of agreement are narrow enough to treat the methods as interchangeable is a clinical/practical judgement, not a statistical one — compare them to a pre-specified maximum acceptable difference.
- The 1.96*SD limits assume the differences are approximately normal and have constant spread across the measurement range; check for proportional bias and heteroscedasticity.
- With small samples the limits of agreement and their confidence intervals are wide and imprecise.
- Results generalize only to the population and measurement range sampled.

## Primary sources

- Bland, J. M., & Altman, D. G. (1986). Statistical methods for assessing agreement between two methods of clinical measurement. The Lancet, 327(8476), 307-310. https://doi.org/10.1016/S0140-6736(86)90837-8
- Bland, J. M., & Altman, D. G. (1999). Measuring agreement in method comparison studies. Statistical Methods in Medical Research, 8(2), 135-160. https://doi.org/10.1177/096228029900800204
- Giavarina, D. (2015). Understanding Bland Altman analysis. Biochemia Medica, 25(2), 141-151. https://doi.org/10.11613/BM.2015.015

## How to cite this

To cite this Clarus method page (the page itself — for the method's own primary sources, see above):

**Plain text**

Clarus, "Bland-Altman method-agreement analysis", version 1.1.0, Clarus method library, 2026. https://clarus.ofrencber.com/library/bland_altman.md

**APA**

Clarus. (2026). Bland-Altman method-agreement analysis (Version 1.1.0) [Statistical method, Clarus method library]. Retrieved from https://clarus.ofrencber.com/library/bland_altman.md

**BibTeX**

```bibtex
@misc{clarus-bland-altman,
  author       = {Clarus},
  title        = {Bland-Altman method-agreement analysis},
  howpublished = {Clarus method library},
  version      = {1.1.0},
  year         = {2026},
  url          = {https://clarus.ofrencber.com/library/bland_altman.md}
}
```

_No DOI is minted for Clarus method pages yet; this citation uses the canonical URL, version and date. Cite the primary sources above for the method's scientific provenance._

---

METHOD SM.RLB.AGR.METH.BLANDALT · VERSION 1.1.0 · UPDATED 2026-06-18 · SOURCE Clarus method library