Power estimation for the Dorfman-Berbaum-Metz method

Rationale and Objectives. The authors describe how to perform power and sample size computations for the Dorfman-Berbaum-Metz method for analyzing multireader receiver operating characteristic (ROC) studies when data from a pilot study or from a previous study similar to the planned study are available. Materials and Methods. Power and sample size computations are described in a step-by-step procedure. Results. To illustrate the power computation method we treat 2 studies that did not show a significant difference between modalities as pilot studies for planning future studies. For the future studies we plan to compare the modalities with respect to the mean of the treatment-reader area under the curve (AUC) estimates. We show how to estimate the reader and case sample sizes for each future study to have 80% power to detect a specified difference in modality AUCs. Conclusions. Application of the power and sample size computation procedure for the Dorfman-Berbaum-Metz method is straightforward. For a given effect size there will be several different reader and case sample size combinations that yield the desired power. It is important that the pilot study or previous study used for the computations be comparable to the planned study with respect to the modalities, reader expertise, case selection, and ratio of normal to abnormal cases.