# What does a Bland-Altman plot show?

## What does a Bland-Altman plot show?

A Bland-Altman plot is a useful display of the relationship between two paired variables using the same scale. It allows you to perceive a phenomenon but does not test it, that is, does not give a probability of error on a decision about the variables as would a test.

## How do you plot a Bland-Altman plot?

Plot a difference plot and limits of agreement.

1. Select a cell in the dataset.
2. On the Analyse-it ribbon tab, in the Statistical Analyses group, click Method Comparison, and then click Bland-Altman.
3. If the data are in 2 variables:
4. If the data are in 2 variables with a separate variable identifying replicates of each item:

What is proportional bias in Bland-Altman?

The Bland-Altman analysis may bring proportional bias, which is present when the difference in values resulting from two methods increases or decreases in proportion to the average values. The Bland-Altman analysis is not an appropriate method to compare repeated measurements.

### Why use a Bland Altman plot?

Bland–Altman plots are extensively used to evaluate the agreement among two different instruments or two measurements techniques. Bland–Altman plots allow identification of any systematic difference between the measurements (i.e., fixed bias) or possible outliers.

### What is proportional bias?

Proportional bias means that one method gives values that are higher (or lower) than those from the other by an amount that is proportional to the level of the measured variable. Investigators sometimes use least squares (Model I) regression analysis to calibrate one method of measurement against another.

What are contract limits?

Limits of agreement estimate the interval within which a proportion of the differences between measurements lie. The limits of agreement includes both systematic (bias) and random error (precision), and provide a useful measure for comparing the likely differences between individual results measured by two methods.

## When do you use a Bland Altman plot?

Create a Bland-Altman plot for method comparison when there is more than one measurement per subject with each laboratory method. The Bland-Altman plot (Bland & Altman, 1986, 1999, 2007), or difference plot, is a graphical method to compare two measurements techniques.

## How to plot the Bland Altman graph in prism?

Plot the Bland-Altman graph The 95% limits of agreement are shown as two dotted lines. These lines are plotted automatically (beginning in Prism 9.1). To manually create lines such as these, double click on the Y axis to bring up Format Axis.

How to make a Bland Altman plot in ggplot2?

Using either base graphics or ggplot2. Produce Bland-Altman Plot Bland-AltmanPlots for assessing agreement between two measuring methods or repeatability (test-retest agreement) of measurements. Using either base graphics or ggplot2.

### Can a Bland Altman plot be produced in SPSS?

What is a Bland-Altman plot, and can one be produced in SPSS? The Bland-Altman plot (Bland & Altman, 1986) is most likely to be seen in the medical statistics literature. 19/02/2019