Association between conservation, secondary structure, positive selection sites and epitopes performed by Fisher’s exact test.

OR: odd ratio; NS: not significant.
Association between (A) Conserved sites and secondary structure (B) sites under positive selection and epitopes and (C) variation (entropy) and epitopes for S protein. (D) association between Conserved sites and secondary structure for P protein. The odds ratio provides a measure of the association between two specified variables. For example, in (A) conserved sites have a strong association with α-helices both in the S (OR = 1.96, P = 0.01) and the P protein (OR = 2.83, P = 3.01e-05<0.01), a weak association with β-sheets in the P protein (OR = 1.94, P = 0.09), but have no significant association between conserved sites and β-sheets in the S protein, indicating the α-helices are highly conserved and the β-sheets can accommodate more variable residues.