Table 1. Multiple sources of variability in microRNA data and literature search [9–84].

Parameter		Source of Variability
Biologic Sample	Tissue	Preservation Method-Formalin fixed-paraffin embedded-Snap Frozen Collection Method-Laser caption microdissection-Macrodissection (includes stroma)
	Plasma	- Collection method (e.g. EDTA tube)-Method to isolate plasma
	Other body fluids (urine, cerebrospinal fluid, etc.)	- Collection method
RNA Extraction	Time to extraction* †	- Immediate (within 24 h)-Delayed
	Method of RNA extraction* †	- Guanidinium thiocyanate-phenol chloroform based (e.g. Trizol LS, LifeTechnologies) -Glass fiber filter-based methods (e.g. miRVANA, Ambion)-Phenol/guanidine-based with and silica membrane based purification (e.g. miRNeasy, Qiagen)
	Type of miRNA*	- Total -Fractional (e.g. exosomal)
miRNA Detection & Statistical Analysis	miRNA characterization	- Cyanine dye-based RT qPCR (SYBR Green) detection-Fluorogenic 5’ nuclease-based RT qPCR detection-Deep sequencing
	Quantification*	- Absolute (addition of exogenous miRNA e.g. C. elegans miRNA)-Relative (use of an internal reference e.g. RNU48, RNU44, RNU47, RNU6, miR-16)
	Cycle threshold bar* †	- Fixed threshold-Variable threshold
	Statistical analysis* †	- Paired t-Test-Wilcoxon Signed Rank test-CT ratios-Rank-based
	Reproducibility†	- Intra-operator comparisons-Inter-operator comparisons

*Items investigated in systematic literature review.

^† Items investigated in our proposed standard methodologic technique.