Coevolution score () based on each characteristic variable.

See Eqs. 24 and 25 for the definitions of and , respectively. The is a threshold for a correlation coefficient corresponding to the E-value (the P-value ) in the Student's t-distribution of the degree of freedom, , where is the number of site pairs, and is the number of OTUs. TP and FP are the numbers of true and false contact residue pairs over all 15 protein families listed in Table 2; protein structures used to calculate contact residue pairs are listed in Table 1. Neighboring residue pairs within 5 residues () along a peptide chain are excluded in the evaluation of prediction accuracy. Also both terminal sites are excluded from counting in this table. PPV stands for a positive predictive value; i.e., . ‡These PPVs are larger than the PPV for concurrent substitutions, i.e., for .