Bland-Altman plot
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In analytical chemistry, a Bland-Altman plot is a method of data plotting used in comparing two different assays (each assay is a procedure to determine how much of a component part is in a mixture). It is identical to a Tukey mean-difference plot, which is what it is still known as in other fields, but was popularized in medical statistics by Bland and Altman.
Consider a set of n samples (for example, objects of unknown volume). Both assays (for example, different methods of volume measurement) are performed on each sample, resulting in 2n data points. Each of the n samples is then represented on the graph by assigning the mean of the two measurements as the abscissa (x-axis) value, and the difference between the two values as the ordinate (y-axis) value.
Hence, the Cartesian coordinates of a given sample S with values of S1 and S2 determined by the two assays is
One common application of the Bland-Altman plot is to compare a new measurement technique with a gold standard.
[edit] References
Bland, J. M., and Altman, D. G. (1986). Statistical methods for assessing agreement between two methods of clinical measurement. Lancet i, 307-310.
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