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Detection accuracy of 0.75 pM target spikes indicated similar performance for the GeneArray 2500 and GeneChip Scanner 3000 across all sites, with statistically significant performance differences favoring the GeneChip Scanner 3000 at Sites 2 and 4, (Figure 4, *). Percent accuracy of Detection across the sites was 74-87% for the GeneChip Scanner 3000, compared to the range of 54-81% for the GeneArray 2500. Scanner Absent call accuracy for the 0.00 pM target spike was statistically higher for the GeneArray 2500 at Site 4 versus the GeneChip Scanner 3000 (Figure 4, **), with all other scanner comparisons indicating equivalence.
Theoretically, it is expected that without spiked transcripts (0.00 pM), Absent call accuracy should approach 100%. However, a range of 88-95% call accuracy was observed for all scanners (Figure 4, 0.00 GeneChip Scanner 3000 and 0.00 GeneArray 2500). The 0.00 pM target spike represents sample in which the 53 cRNA transcripts were shown to be Absent by previous GeneChip expression assays. An explanation for the apparent discrepancy in the Absent call accuracy is that some of these transcripts may be expressed at a low level and thus, are occasionally detected.
Evaluation of the 53 spiked transcripts showed that a subset of these transcripts was frequently called Present or Marginal in the 0.00 pM target sample across the scanner types and sites. Taqman RT-PCR analysis was performed to examine the possibility of endogenous levels of all 53 transcripts. This analysis showed marginal evidence of expression
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