Invariant sets and normalization curves generated by nonlinear normalization methods using identical randomly chosen arrays, (a) Invariant-feature method, x-axis, Mature B cells, replicate 3, not normalized; y-axis, baseline: pre-BI cells, replicate 2. Black dots, feature intensities; red circles, invariant set of features (connected by the green line). The blue line forms the diagonal with slope of I. (b) Invariant set method. Cells as in (a). Black dots, probe set average difference values; red circles, invariant set. Blue dots form the diagonal with slope of I. Axes are labeled with average difference intensities.