Scale factor for an Affymetrix chip is the ratio between the trimmed mean of the
expression values for that chip and the target intensity (in our case 100).
A similar value was computed for the non-Affymetrix chips (target intensity/ median expression value)
Percent Present is the number of probes called present on the array divided by
the total number of probes. A description of how calls were generated for
non-Affymetrix chips is detailed in the normalization section.
For Affymetrix chips, the GapDH and Beta Actin 5’3’ ratios were computed based on MAS5 expression values.
QC Metric Distributions
While no hard cutoffs were applied for each of the QC metrics,
we examined the distribution of the metrics to determine if samples appeared to be outliers.
Principal components analysis (PCA) and clustering were used to visualize the
relationship between the samples and determine if one or more samples appeared to be outliers.