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.