Relationship between mean log₁₀(AI) and mean variance log₁₀(AI) for the five NOD-derived strains (NOD,Idd3, Idd5, Idd3/5, Idd9). Probe sets were ordered according to their mean log₁₀(AI) value across the five strains and assigned to successive, nonoverlapping bins of 500 probe sets. Variance across the five strains was calculated for each probe set independently, and the mean for each bin is plotted against the mean log₁₀(AI) for that bin. As only a small proportion of genes were expected to be genuinely differentially expressed between the strains, the resulting pattern was anticipated to be representative of the underlying relationship between variance and log₁₀(AI). The data shown are representative of both replicate experiments.