title: CGHpower: exploring sample size calculations for chromosomal copy number experiments.
abstract: BACKGROUND
  Determining a suitable sample size is an important step in the planning of microarray experiments. Increasing the number of arrays gives more statistical power, but adds to the total cost of the experiment. Several approaches for sample size determination have been developed for expression array studies, but so far none has been proposed for array comparative genomic hybridization (aCGH).
  
  
  RESULTS
  Here we explore power calculations for aCGH experiments comparing two groups. In a pilot experiment CGHpower estimates the biological diversity between groups and provides a statistical framework for estimating average power as a function of sample size. As the method requires pilot data, it can be used either in the planning stage of larger studies or in estimating the power achieved in past experiments.
  
  
  CONCLUSIONS
  The proposed method relies on certain assumptions. According to our evaluation with public and simulated data sets, they do not always hold true. Violation of the assumptions typically leads to unreliable sample size estimates. Despite its limitations, this method is, at least to our knowledge, the only one currently available for performing sample size calculations in the context of aCGH. Moreover, the implementation of the method provides diagnostic plots that allow critical assessment of the assumptions on which it is based and hence on the feasibility and reliability of the sample size calculations in each case.The CGHpower web application and the program outputs from evaluation data sets can be freely accessed at http://www.cangem.org/cghpower/
authors.affiliation: Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Ilari
authors.initials: I
authors.lastname: Scheinin
authors.forename: José A
authors.initials: JA
authors.lastname: Ferreira
authors.forename: Sakari
authors.initials: S
authors.lastname: Knuutila
authors.forename: Gerrit A
authors.initials: GA
authors.lastname: Meijer
authors.forename: Mark A
authors.initials: MA
authors.lastname: van de Wiel
authors.forename: Bauke
authors.initials: B
authors.lastname: Ylstra
mesh_terms: D000818:Animals; D002869:Chromosome Aberrations; D002877:Chromosomes, Human; D055028:Comparative Genomic Hybridization / Q000379:methods* / Q000706:statistics & numerical data; D003198:Computer Simulation; D020869:Gene Expression Profiling; D006801:Humans; D009369:Neoplasms / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D018401:Sample Size