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Table 3 Variability in miRNA expression measurements: technical replicates, biological replicates, and frozen versus FFPE tissue

From: MicroRNA Expression in Formalin-fixed Paraffin-embedded Cancer Tissue: Identifying Reference MicroRNAs and Variability

    Variability, SD (Cq)
   Correlationa, r s Raw data Total variability with normalized data
  Samples median (range) Individual miRNA Inter-sample Total Global mean Optimal number of refs. (n = 4) Two best refs.
Technical replicates 5 0.995 (0.993–0.996) 0.24 0.19 0.31 0.24 0.32 0.40
Biological replicates 4 0.985 (0.98–0.99)b 0.42 0.30 0.52 0.42 0.46 0.49
Frozen vs. FFPE 17c 0.92 (0.66–0.96) 1.35 1.00 1.68 1.18 1.35 1.31
  1. a For frozen versus FFPE, the correlations were calculated between formalin-fixed and corresponding frozen samples (12 total correlations).
  2. b The median correlation between unrelated biological replicates, i.e. the inter-individual correlation, was 0.88 (range 0.84–0.91).
  3. c Sample distribution: 5 frozen, 4 x 2-day fixation, 5 x 3-day fixation, and 3 x 6-day fixation.
  4. Abbreviations: FFPE, formalin-fixed paraffin-embedded; SD, standard deviation; Cq, quantification cycle; r s , Spearman's rank correlation coefficient; refs., references.
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