Bleeding: cancer and polyp comparison. crc = colorectal cancer. The horizontal and vertical dimensions of the each ellipse are proportional to the square root of the number of non-diseased and diseased respectively. + shows the expected sensitivity and 1-specificity for the curve. The paired points (one black and one open joined by a dotted line) represent a within study comparison. The diagonal line joining (0,0) and (1,1) represents an ROC of no diagnostic value.