Table 1.

Results for standards^a

Standard	Nominal log10 concnb	Real-time PCR				Digital PCR				Variability (P value)
		No. of positive specimens/total no. of attempts	Mean viral load (log10 no. of copies/ml)	SD	% CV	No. of positive specimens/total no. of attempts	Mean viral load (log10 no. of copies/ml)	SD	% CV
AcroMetrix	2.48	9/9	2.11	0.34	16.11	7/7c	2.23	0.24	10.76	0.409
AcroMetrix	3.48	9/9	3.15	0.12	3.81	8/8c	3.06	0.08	2.61	0.248
AcroMetrix	4.48	9/9	4.19	0.12	2.86	8/8c	4.16	0.03	0.72	0.003
AcroMetrix	5.48	9/9	5.25	0.07	1.33	9/9	5.19	0.03	0.58	0.048
NIST	1	0/9	0	0	NA	1/9	0.27	0.82	303.7	NA
NIST	2	7/9	1.09	0.67	61.47	3/9	0.83	1.24	149.4	0.104
NIST	3	9/9	2.35	0.23	9.79	7/9	2.1	1.2	57.14	<0.001
NIST	4	9/9	3.29	0.09	2.74	9/9	3.66	0.1	2.73	0.637
NIST	5	9/9	4.34	0.05	1.15	9/9	4.63	0.07	1.51	0.348
NIST	6	9/9	5.35	0.06	1.12	9/9	5.6	0.05	0.89	0.394
NIST	6.7	9/9	6.1	0.11	1.8	9/9	6.21	0.08	1.29	0.345
WHO	1	6/9	1.17	0.91	77.78	1/7c	0.29	0.76	262.07	0.660
WHO	2	9/9	2.18	0.38	17.43	3/7c	0.91	1.14	125.27	0.008
WHO	3	9/9	3.16	0.11	3.48	9/9	2.71	0.1	3.69	0.727
WHO	4	9/9	4.14	0.11	2.66	8/8c	3.77	0.04	1.06	0.007
WHO	5	9/9	5.13	0.07	1.36	9/9	4.75	0.02	0.42	0.004
WHO	6	9/9	5.99	0.05	0.83	8/8c	5.72	0.02	0.35	0.020

^aThe number of positive specimens/number of attempts, the mean log-transformed measurements, and standard deviation of the log-transformed measurements are given for each technology at each concentration of each standard. Bartlett's test was used to compare the variability of the two technologies, based on the SD. A small-variability P value indicates that there is significant evidence that the two technologies do not have equal standard deviation in their measurements. CV, coefficient of variation; NA, not available.

^bNominal concentrations in IU/ml for AcroMetrix and WHO standards and number of copies/ml for NIST standards.

^cDecreased replicates due to failure of the instrument (either failed to generate or read the droplet).