Metrics of EAA
The cell and tissue specificity of DNAm also has implications for the
calculation of EAA.
In blood data, there are two prominent measures of EAA: Intrinsic
Epigenetic Age Acceleration (IEAA) and Extrinsic Epigenetic Age
Acceleration (EEAA). IEAA is used in conjunction with the Horvath
pan-tissue clock and treats cell type proportions as confounders,
highlighting “intrinsic aging processes”, which are not influenced by
cell type composition changes. EEAA is used to assess EAA from Hannum
clock age estimates. Since this clock was developed solely using blood
samples and its results have been shown to reflect changes in cell type
compositions, EEAA represents changes in the immune
system.77. Other
commonly used methods for assessing EAA are the difference between EA
and CA and the residual of the regression of EA on CA.