Efficiency is the proportion of SNP and non-SNP sites identified correctly as compared with the canonical dideoxy sequence, either at high or low efficiency. Accuracy is the proportion of SNPs identified correctly. Correct and erroneous calls may be made at either high or low confidence, differentiated by dS/N= 0.20 (see Methods and Figure 2). The table is equivalent to a conventional 2 × 2 contingency table, with the categories on the second line transposed. This arrangement emphasizes the column totals of correct versus incorrect calls, and the assignment of low-confidence incorrect calls as N s, in Tables 3, 4, and 5.