Bland-Altman diagram

Example of a Bland-Altman diagram

The Bland-Altman diagram (syn. Md plot ) - named after John Martin Bland and Douglas G. Altman - is a graphic representation method for comparing two measurement methods and . In this special form of a point diagram , the differences between the two measurement methods (or, alternatively, the ratio ) are plotted against the mean value of the two methods. In a Cartesian coordinate system , the Bland-Altman diagram is given by the graph ${\displaystyle S_{1}}$ ${\displaystyle S_{2}}$ ${\displaystyle S_{1}-S_{2}}$ ${\displaystyle {\tfrac {S_{1}}{S_{2}}}}$ ${\displaystyle {\tfrac {S_{1}+S_{2}}{2}}}$

${\displaystyle S(x,y)=\left({\frac {S_{1}+S_{2}}{2}},(S_{1}-S_{2})\right)}$.

For easier interpretation, three additional lines are shown:

• Mean of the difference
• Mean of the difference plus 1.96 * standard deviation of the difference
• Mean of the difference minus 1.96 * standard deviation of the difference

This diagram provides a visual assessment

• how high the fluctuation range of the deviations is,
• whether one measuring method in principle measures higher or lower than the other (systematic measuring error),
• whether the deviation of the methods or the spread of the deviations depends on the level of the values. For the latter, a logarithmic representation of the measured values ​​is meaningful.

The diagram is mainly used to compare new measurement methods with a gold standard .

literature

• JM Bland, DG Altman: Statistical methods for assessing agreement between two methods of clinical measurement. In: Lancet. 1, Feb 8, 1986, pp. 307-310. PMID 2868172
• JM Bland, DG Altman: Measuring agreement in method comparison studies. In: Stat Methods Med Res. 8, Jun 1999, pp. 135-160. PMID 10501650

Web links

• Items to Bland-Altman plot (English)
• Website of JM Bland (English)
• Instructions for creating a Bland-Altman plot in SPSS (English)
• Instructions for creating a Bland-Altman plot in R (English)