Effect of normalization methods on the classification accuracy. Microarray experiments were developed using Agilent rat whole genome array (4 X 44 k). Cultured primary hepatocytes were treated with distinctive 105 compounds (Additional file 1) as well as respective vehicle controls for 24 h; subsequently RNAs were isolated for array hybridization. 105 compounds treated samples and control samples were divided into 14 classes. Two normalization methods (median and control) based normalizations were compared for the classification accuracy of the 14 classes.