Bland–Altman plot

The Bland -Altman plot ( Syn md- plot) - named after John Martin Bland and Douglas G. Altman - is a graphical representation method for comparing two measurement methods and. In this special form of a scatter plot of both methods, the differences (or alternatively, the ratio) versus the average of the two methods. In a Cartesian coordinate system, the Bland Altman chart is given by the graph

.

For ease of interpretation, three additional lines are displayed:

• Average of the difference
• Average of the difference plus 1.96 standard deviation of the difference
• Average of the difference minus 1.96 standard deviation of the difference

This diagram provides a visual assessment

• How high the range of variation of the deviations is
• Whether a measurement method in principle be higher or lower than the other measures ( systematic measurement error ),
• If the deviation of the methods or the dispersion of the deviation of the amount of the values ​​depends. For the latter, a logarithmic representation of the measured values ​​is meaningful.

The diagram is mainly used for the comparison of new measurement method with a gold standard.