title: A web application for sample size and power calculation in case-control microbiome studies.
abstract: : When designing a case-control study to investigate differences in microbial composition, it is fundamental to assess the sample sizes needed to detect an hypothesized difference with sufficient statistical power. Our application includes power calculation for (i) a recoded version of the two-sample generalized Wald test of the 'HMP' R-package for comparing community composition, and (ii) the Wilcoxon-Mann-Whitney test for comparing operational taxonomic unit-specific abundances between two samples (optional). The simulation-based power calculations make use of the Dirichlet-Multinomial model to describe and generate abundances. The web interface allows for easy specification of sample and effect sizes. As an illustration of our application, we compared the statistical power of the two tests, with and without stratification of samples. We observed that statistical power increases considerably when stratification is employed, meaning that less samples are needed to detect the same effect size with the same power.
  
  
  
  The web interface is written in R code using Shiny (RStudio Inc., 2016) and it is available at https://fedematt.shinyapps.io/shinyMB The R code for the recoded generalized Wald test can be found at https://github.com/mafed/msWaldHMP CONTACT: Federico.Mattiello@UGent.be.
authors.affiliation: Department of Mathematical Modelling, Statistics and Bioinformatics, Ghent University, Coupure Links 653, Gent, 9000.
authors.forename: Federico
authors.initials: F
authors.lastname: Mattiello
authors.affiliation: Janssen Pharmaceutica, Turnhoutseweg 30, Beerse, 2340, Belgium.
authors.forename: Bie
authors.initials: B
authors.lastname: Verbist
authors.affiliation: KU Leuven, Laboratory of Molecular Bacteriology and Department of Microbiology and Immunology, Herestraat 49, Leuven, 3000, Belgium.
authors.forename: Karoline
authors.initials: K
authors.lastname: Faust
authors.affiliation: KU Leuven, Laboratory of Molecular Bacteriology and Department of Microbiology and Immunology, Herestraat 49, Leuven, 3000, Belgium.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Raes
authors.affiliation: BioRankings, 4041 Forest Park Ave, St.Louis, MO 63108, USA.
authors.forename: William D
authors.initials: WD
authors.lastname: Shannon
authors.affiliation: Janssen Pharmaceutica, Turnhoutseweg 30, Beerse, 2340, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: Bijnens
authors.affiliation: Department of Mathematical Modelling, Statistics and Bioinformatics, Ghent University, Coupure Links 653, Gent, 9000 University of Wollongong, National Institute for Applied Statistics Research Australia (NIASRA), School of Mathematics and Applied Statistics, Australia.
authors.forename: Olivier
authors.initials: O
authors.lastname: Thas
mesh_terms: D016022:Case-Control Studies; D019295:Computational Biology / Q000379:methods*; D006801:Humans; D020407:Internet; D064307:Microbiota; D008962:Models, Theoretical; D018401:Sample Size; D012984:Software