Characterization of epistatic pairs in subtype H3N2 surface proteins, compared to expectations for randomly chosen pairs.

are obtained from two-tailed tests, except for the last two rows which report one-sided tests regarding distances between sites. Single and double asterisks denote significance at 0.05 and 0.01 level, respectively; “ns”, “ept”, “npt”, “obs”, “exp”, and “N/A” denote not significant, epitopic, non-epitopic, observed, expected, and not applicable respectively. 1 distances are computed only over those significant pairs in which both residues are present in the crystal structure (see “Materials and Methods”).