Figure 2From: A simple method to combine multiple molecular biomarkers for dichotomous diagnostic classificationThe performance index (P i ) derived from the area under the ROC curve of the biomarkers within each dataset. The curves demonstrate that the diagnostic performance of the biomakers follows the Zipf's law. The colors for the four datasets are used consistently in Figure 3 and Supplementary Figures 1 and 2 (see additional file 1).Back to article page