Table 1.

2 × 2 contingency table for one particular gene in E. coli

	Conserved sites	Non-conserved sites
Structurally sensitive	3	10
Structurally non-sensitive	4	57

Note - The odds ratio of conservation pattern between structurally disruptive and non-disruptive sites is (3/10)/(4/57) = 4.28. Because there is one contingency table per gene, we applied the Mantel-Haenszel test to compute the joint odds ratio across all genes.