title: Improving power to detect changes in blood miRNA expression by accounting for sources of variability in experimental designs.
abstract: BACKGROUND
  Blood miRNAs are a new promising area of disease research, but variability in miRNA measurements may limit detection of true-positive findings. Here, we measured sources of miRNA variability and determine whether repeated measures can improve power to detect fold-change differences between comparison groups.
  
  
  METHODS
  Blood from healthy volunteers (N = 12) was collected at three time points. The miRNAs were extracted by a method predetermined to give the highest miRNA yield. Nine different miRNAs were quantified using different qPCR assays and analyzed using mixed models to identify sources of variability. A larger number of miRNAs from a publicly available blood miRNA microarray dataset with repeated measures were used for a bootstrapping procedure to investigate effects of repeated measures on power to detect fold changes in miRNA expression for a theoretical case-control study.
  
  
  RESULTS
  Technical variability in qPCR replicates was identified as a significant source of variability (P < 0.05) for all nine miRNAs tested. Variability was larger in the TaqMan qPCR assays (SD = 0.15-0.61) versus the qScript qPCR assays (SD = 0.08-0.14). Inter- and intraindividual and extraction variability also contributed significantly for two miRNAs. The bootstrapping procedure demonstrated that repeated measures (20%-50% of N) increased detection of a 2-fold change for approximately 10% to 45% more miRNAs.
  
  
  CONCLUSIONS
  Statistical power to detect small fold changes in blood miRNAs can be improved by accounting for sources of variability using repeated measures and choosing appropriate methods to minimize variability in miRNA quantification.
  
  
  CONCLUSIONS
  This study demonstrates the importance of including repeated measures in experimental designs for blood miRNA research. See all the articles in this CEBP Focus section, "Biomarkers, Biospecimens, and New Technologies in Molecular Epidemiology."
authors.affiliation: Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California. sdaniels@berkeley.edu.
authors.forename: Sarah I
authors.initials: SI
authors.lastname: Daniels
authors.affiliation: Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California.
authors.forename: Fenna C M
authors.initials: FC
authors.lastname: Sillé
authors.affiliation: Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California.
authors.forename: Audrey
authors.initials: A
authors.lastname: Goldbaum
authors.affiliation: Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California.
authors.forename: Brenda
authors.initials: B
authors.lastname: Yee
authors.affiliation: Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California.
authors.forename: Ellen F
authors.initials: EF
authors.lastname: Key
authors.affiliation: Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California.
authors.forename: Luoping
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California.
authors.forename: Martyn T
authors.initials: MT
authors.lastname: Smith
authors.affiliation: Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California.
authors.forename: Reuben
authors.initials: R
authors.lastname: Thomas
mesh_terms: D064368:Healthy Volunteers; D006801:Humans; D035683:MicroRNAs / Q000097:blood* / Q000378:metabolism; D012107:Research Design
chemical_list: D035683:MicroRNAs