# Create Bland-Altman plot online

To create a Bland-Altman plot (often referred to as the difference plot), you only need to select two metric variables.

To create a Bland-Altman analysis, two dependent samples are needed. On the x-axis of the Bland-Altman plot, the mean value of the pairs of values is then plotted and on the y-axis the difference between the pairs is plotted, thus creating a scatter plot.

Bland and Altman point out that two methods measuring the same parameter have a good correlation. If enough data is available, it is possible to detect a systematic measurement error, which is plotted in the Bland-Altman plot by the mean of the differences.

## Bland-Altman plot

A Bland-Altman plot, also known as a difference plot, is a graphical method used to
compare two measurement techniques or to assess the agreement between two sets of data.
The plot shows the difference between the two measurements on the *y* axis and the average
of the two measurements on the *x* axis.

The plot consists of a scatter plot of the differences between the two measurements against the averages of the two measurements, with a horizontal line representing the mean difference and lines representing the standard deviation from the mean difference. The plot allows the visualization of the agreement between the two methods and any systematic bias or random error.

It's widely used in medical research, industrial quality control and other fields where comparing multiple measurement methods is required. It's also useful to identify outliers, and for interpreting the agreement between a new measurement technique and a gold standard.