Sample size: CI of Area under ROC curve
Command: | Sample size![]() ![]() ![]() ![]() |
Description
Calculates the required sample size for the for the estimation of a confidence interval of the Area under the ROC curve (AUC).
Required input
- Confidence level (%): select the confidence level: 90, 95 or 99%. A 95% confidence level (the value for a 95% confidence interval) is the most common selection. You can enter a different confidence level if required.
- Area under ROC curve: the hypothesized Area under the ROC curve (the AUC expected to be found in the study).
- Desired Lower or Upper bound of the confidence interval: this value defines the desired width of the confidence interval. If your aim is to show that the AUC is larger than a certain value, enter the value of the Lower bound; if your aim is to show that the AUC is lower than a certain value, enter the value for the Upper bound.
- Ratio of sample sizes in negative / positive groups: enter the desired ratio of negative and positive cases. If you desire both groups to have an equal number of cases you enter 1; when you desire twice as many cases in the negative than in the positive group, enter 2.
Example
You want to show that an observed AUC of 0.63 test is significantly higher than the value 0.5, then you enter 0.63 for Area under ROC curve and 0.5 for Desired Lower bound of the confidence interval. You expect to include an equal number of negative and positive cases, so for the Ratio of sample sizes in negative / positive groups you enter 1.
Click Calculate
In the example a total of 64 cases are needed, 32 cases in the negative and 32 in the positive group.
The program uses an iterative procedure to calculate the sample sizes.