TABLE 2.

Phase 1 results from seven laboratories for N in R1, R2, and dilutions A to D^a

Sample (dilution)	N
	Laboratory 1a	Laboratory 1b	Laboratory 2	Laboratory 3	Laboratory 4	Laboratory 5	Laboratory 6b	Endpoint titer laboratory 7c
R1	5.5 × 108	5.5 × 108	2.2 × 109	4.3 × 108	1.6 × 109	4.0 × 108	1.2 × 107	1:1,000
A (1:64)	2.4 × 107 (1:23)d	3.2 × 107 (1:17)	1.1 × 108 (1:20)	4.3 × 105b (1:1,000)	3.0 × 107 (1:53)	1.1 × 107 (1:35)	8.2 × 105 (1:14)	1:128
B (1:64,000)	1.1 × 104 (1:50,000)	2.1 × 104 (1:26,000)	4.8 × 104 (1:46,000)	4.3 × 103e (1:100,000)	<5 × 106	<2.9 × 106	6.6 × 102 (1:17,900)	Negative
R2	8.6 × 108	5.2 × 108	4.7 × 109	4.3 × 108	2.0 × 109	3.4 × 108	2.7 × 106	1:>100
C (1:32)	5.5 × 107 (1:16)	1.3 × 107 (1:39)	1.3 × 108 (1:36)	4.3 × 107e (1:10)	5.2 × 107 (1:38)	1.1 × 107 (1:30)	3.4 × 105 (1:8)	1:32
D (1:32,000)	3.0 × 104 (1:28,700)	9.3 × 104b (1:5,600)	1.7 × 105 (1:28,000)	1.4 × 104e (1:30,000)	<5 × 106	<2.9 × 106	1.2 × 103 (1:2,390)	Negative
No. of replicates per dilution step	7	7	11–16	2

^aLaboratories 1 to 3 used nested PCR and limiting dilution; laboratories 4 to 7 used reference samples. 

^bData not considered for further evaluation because of fourfold or greater deviation from the true dilution factor. 

^cEndpoint titer of a hybridization assay. 

^dValues in parentheses are dilution factors determined by the laboratories. 

^eDue to low numbers of replicates, these data were not considered for calculation of the GMV.