Normalization of hybridization data from samples mimicking heterogeneous cell populations and single copy alterations. Array CGH data were generated for samples mimicking single copy loss (deletion) or single copy gain (amplification) with contamination of increasing proportion of reference DNA, indicated as percentage on the horizontal axis. The experimental procedure for the array CGH experiments was previously described . Global median normalization (method 1), stepwise normalization (method 12), global median normalization with background subtraction (method 13), and 3 step normalization with background subtraction (method 19) were applied. T-statistic values computed before and after normalization for arrays T1-T10 are summarized.