Table 4. Sensitivity and specificity in detection of rare mutations.

Dilution	Total Reads	Mutated Reads (G)	Observed Frequency (%G)	Expected Frequency (%G)	Positions with Errors	Specificity
1∶1,000	151,118	110	0.073	0.1	0	1.00
1∶2,000	148,990	56	0.038	0.05	0	1.00
1∶5,000	144,307	30	0.021	0.02	6	0.96
1∶10,000	161,921	19	0.012	0.01	24	0.85

For each dilution value, the total number of sequenced reads, the number of reads bearing the mutated allele (G), and the observed and expected substitution frequency are reported. We considered errors all positions showing a substitution frequency equal to or higher than the corresponding frequency of the mutated allele. This allowed measuring of the specificity, defined as the number of true negatives (156−errors) over all variable positions (156).