Linear regression plots of the log transformed %BCR-ABL/control gene values obtained from all laboratories for the 4 reference materials (Sample 1, BCR/ABL 1 08/192; Sample 2, BCR/ABL 2 08/194; Sample 3, BCR/ABL 3 08/196; and Sample 4 BCR/ABL 4 08/198). Regression plots are shown for each control gene, shown before and after conversion to the IS.