These strategies appear unsuitable for standardization and quality control of RNA integrity assessment, which require simple but consistent expert-independent classification, facilitating information exchanges between laboratories. The N-value corresponds to the number of samples by category. The mean quality metrics, i.e. RIN and DegFact and the mean fold change (2 ÀDDCt ) relative to the reference sample are indicated, together with the 95% confidence intervals. Observed technical variation (IC-rep, P = 0.05) is also specified, considering duplicate (two per gene per target sample) and replicate (six per gene per calibrator sample) measures. The reference sample exhibits a RIN of 9, a DegFact value of 4.9 and by default mean fold change set to 1. The observed decrease in the expression (relative expression, %) relative to the reference sample is calculated. The fold differences refer to the fold-ratios that are expected in the expression levels for a gene, across categories (between categories), given that the samples only differ by their quality, and within each category (within categories), considering RNA of comparable integrity. The fold-ratios (technical variation) that may be expected by chance in the gene expression levels, P = 0.05, from some technical reasons, are also considered.