Differentially variable and differentially methylated CpGs. (a) Histograms of P-values derived from Bartlett's test comparing differences in variance between normal samples that become neoplastic (CIN2+) and samples that remain normal (differentially variable CpGs (DVCs)). (b) Histograms of P-values derived from t-tests comparing differences in mean CpG methylation levels between the same two phenotypes (differentially methylated CpGs (DMCs)). (c) Scatterplot of Bartlett statistics (logarithm of the ratio of the variance in prospective CIN2+ to that in normal) shown on the y-axis against the corresponding t-statistics (x-axis) for the top 500 DVCs. The numbers of hypervariable (hyperV) and hypovariable (hypoV) DVCs are given. (d) Typical methylation profile of a hypervariable DVC (blue = prospective CIN2+, green = normal). The thin dashed lines indicate the mean levels of methylation in each phenotype. The P-values shown are from a Bartlett's test (differential variability) and t-test (differential methylation).