Correlation between paired fresh-frozen and formalin-fixed paraffin-embedded tumour samples on the EPIC array. a Density plot of β values from the EPIC array for fresh-frozen (FF) and formalin-fixed paraffin-embedded (FFPE) samples restored with either Infinium or REPLI-g. Correlation of β values between paired FF and FFPE paediatric brain tumour samples illustrating the sample with b the lowest and c the highest Pearson correlation respectively. d Pearson correlation between paired FF and FFPE samples plotted against the proportion of CpG sites with β values in the low-middle range (between 0.2 and 0.4). e Pearson correlation between paired FF and FFPE samples plotted against a noise estimate from FFPE copy number alterations (CNAs) indicating a trend of worse correlation with increasing noise. CNA plots for the FF (upper panel) and paired FFPE sample (lower panel) with f the lowest and g the highest Pearson correlation respectively.