Fig. 1

Construction of the probabilistic 2D kernel age predictor. A The association of DNA methylation (DNAm) with chronological age is exemplarily depicted for the CpG sites cg00329615 for all the samples in the training set. B 2D density kernel of the scatter plot depicted in A. The horizontal line exemplarily depicts the DNAm level of a given sample. C Density distribution as estimated for the probability of age-predictions for the sample depicted in B. D Joint probability for 27 age-associated CpGs for the same sample. E Performance of the methodology shown A–D for all the samples in the training set (color code indicates different studies of the training set). F Histogram of the ages in the training set. G Normalization of 2D kernels by age (divided by the corresponding value in the histogram). H Density distribution for the exemplary sample (line) in G. I Joint probability for 27 CpGs after normalization by age. J Performance of the methodology shown F–I for all the samples in the training set. K Alternatively, the training set was split in 5-year bins from 0 to 90 years (plus one bin of samples older than 90 years) and 15 samples from each bin were taken. The Scatter plot again depicts this selection for cg00329615. L 2D density kernel of K. M Density distribution for the sample in panel L. N Joint probability for 27 CpGs of the same sample. O Performance of the methodology shown K–N for all the samples in the training set