# Bland-Altman Analysis Calculator

> Free Bland-Altman calculator. Paste paired measurements from two methods and get the bias, the 95% limits of agreement with their confidence intervals, the Bland-Altman plot, a sentence for your manuscript and R code.

Canonical: https://biostatkit.com/bland-altman

Paste pairs of measurements made by two methods and get the bias, the 95% limits of agreement with their confidence intervals, the Bland-Altman plot, a sentence you can paste into your manuscript, and the R code that reproduces the numbers.

## Methods wording

Agreement between the two methods was assessed with BiostatKit [1] using a Bland-Altman analysis [2]: the mean difference and the 95% limits of agreement (mean difference plus or minus 1.96 SD), with 95% CIs from the t distribution.

Method: Bland-Altman bias and 95% limits of agreement, with CIs from the t distribution (Bland and Altman, 1999).

## Frequently asked questions

### What do the limits of agreement mean?

If the differences are roughly normal, about 95% of the differences between the two methods fall between the lower and the upper limit. If that range is narrower than the difference you can accept in practice, the methods can be used interchangeably.

### How many pairs do I need?

There is no fixed number. The confidence intervals of the limits show the precision: with 20 pairs each limit is uncertain by roughly 0.8 SD either side, with 100 pairs by roughly 0.3 SD.

### When should I use the percentage difference?

When the scatter of the differences grows with the size of the measurement, for example blood levels that range over several fold. The percentage difference puts the limits on a relative scale.

### Bland-Altman or ICC?

A Bland-Altman analysis shows how far apart two methods can be in the original unit. The ICC gives one number for reliability. Many method-comparison papers report both.

### Is my data stored or sent anywhere?

No. All calculations run in your browser tab. Nothing is uploaded, and the page works offline once loaded.

## Related calculators

- [Intraclass correlation (ICC)](https://biostatkit.com/icc)
- [Cohen's kappa](https://biostatkit.com/cohens-kappa)

Author: TS.BS. Vũ Duy Kiên (https://www.vuduykien.com)