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Sample size: comparison of two ROC curves

Command:Sample size
Next selectComparison of two ROC curves


Calculates the required sample size for the comparison of the areas under two ROC curves (derived from the same cases). The sample size takes into account the required significance level and power of the test (see Sample size calculation: Introduction).

Required input


Sample size calculation for the comparison of two ROC curves.

You are interested to show that the discriminating power of two assays (performed on the same cases), with an area under the ROC curve of 0.825 and 0.9, is significantly different. From previous studies you know that the rank correlation between the two assays is 0.4 in both positive and negative cases.

You enter the values 0.825 and 0.9 for Area under ROC curve 1 and Area under ROC curve 2. Next you enter 0.4 for Correlation in positive group and Correlation in negative group.

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 sample size.

In the example 133 cases are required in the positive group and 266 in the negative group, giving a total of 399 cases.

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


See also