Data evaluation I assaytoassay variability

The reliability of qPCR assays was first evaluated by testing the same samples repeatedly, at intervals ranging from one week to three months (see Figure 10.2). In 75 genomic DNA samples treated with EcoR I and BstU I, correlation analyses were done in a subset of samples (n = 46-70) with methylation levels >0.01 (other samples were treated as uninformative). For promoter fragment 1 (n = 70 informative observations), MDR1 sequences with methylated BstU I site accounted for 1% to 40% of the total DNA (see Figure 10.2A). The results obtained from two separate experiments were highly consistent, with a correlation coefficient (r) = 0.93 (P <0.001), regardless of certain differences (e.g. gender and the amount of input DNA) in the source materials used for qPCR (adjusted r > 0.90, P <0.001). Results obtained from MDR1 intron 1 qPCR assays were similar (see Figure 10.2B), except that fewer samples (n = 46) could be analyzed for assay-to-assay variability.

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