Comparison of ideal samples by the signed KS test. (A) The distributions have different locations. The lines represent the empirical cumulative distributions of each sample (the reference sample is plotted as a bold line). The KS statistic is the maximum vertical distance between the curves and is indicated by the vertical red line. As the reference sample is on the left, the arrow points downwards, so the statistic is negative. (B) The distributions have different variances. In this example there are two positions where the vertical distance is at a maximum, indicated by the two red lines. As the arrows point in opposite directions, the sign of the KS statistic is not defined.