We next sought to characterize the overall variability of each chromatin state across the full range of cell and tissue types. We first evaluated the observed consistency of each chromatin state at any given genomic position across all 127 epigenomes (Fig. 5a). We found that H3K4me1-associated states (including TxFlnk, EnhG, EnhBiv, Enh) are the most tissue-specific, with 90% of instances present in at most 5-10 epigenomes, followed by bivalent promoters (TssBiv), and repressed states (ReprPC, Het). In contrast, active promoters (TssA) and transcribed states (Tx, TxWk) were highly constitutive, with 90% of regions marked in as many as 60-75 epigenomes, and quiescent regions (Quies) were the most constitutive, with 90% of Quies regions consistently marked as Quies in most of the 127 epigenomes. These results held in the 18-state chromatin state model (Extended Data 5a), and in the subset of highest-quality epigenomes (Fig. S6a,b).
