ROC analysis. The x-axis is the rate of false positives (in log10), computed as the proportion of autosomal markers that have copy number below any given threshold (for the 1X calculation). The y-axis depicts sensitivity, defined as the proportion of X chromosome markers that have copy number values below the same threshold (for the 1X calculation). The curve is generated by calculating these values at many different thresholds. The curves from the 3X, 4X, and 5X cell lines were generated in an analogous fashion.