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Sample size calculation: Bland-Altman plot

Command:Sample size
Next selectBland-Altman plot


Calculates the required sample size for a method comparison study using the Bland-Altman plot.

In this method, limits of agreement (LoA) are calculated as the mean of differences between two measurements ± 1.96 x their standard deviation (Bland & Altman, 1986)

Two methods are considered to be in agreement when a pre-defined maximum allowed difference (Δ) is larger than the higher limit of agreement, and -Δ is lower than the lower limit of agreement.

Proper interpretation takes into account the 95% confidence interval of the LoA, and to be 95% certain that the methods do not disagree, Δ must be higher than the upper 95 CI limit of the higher LoA and -Δ must be less than the lower %95 CI limit of the lower LoA:

Schematic presentation of Bland-Altman plot.

To show that two methods are in agreement, an adequate sample size must be established to have a high probability (power) that Δ will fall outside the 95 CI of the Limits of Agreement.

Required input


You want to show that two laboratory methods are in agreement. A preliminary study has shown that the mean difference is 0.001167, and the standard deviation of the differences is 0.001129. The maximum allowed difference between the methods is 0.004 units (example by Lu et al., 2016).

You enter 0.001167 for Expected mean of differences, 0.001129 for Expected Standard Deviation of differences and 0.004 for Maximum allowed difference between methods.

For α-level you select 0.05 and for β-level you select 0.20 (power is 80%).


After you click Calculate the program displays the required total number of cases in the study. The calculation may take some time to complete.

For the example the minimum required total sample size is 83.

A table shows the required sample size for different Type I and Type II Error levels.

Sample size calculation for Bland & Altman plot.

MedCalc uses the method by Lu et al. (2016) to calculate the sample sizes.

Note that the Bland-Altman plot implemented by MedCalc (and as described in Bland & Altman, 1986) has a fixed alpha level of 0.05.


See also