title: A statistical assessment of differences and equivalences between genetically modified and reference plant varieties.
abstract: BACKGROUND
  Safety assessment of genetically modified organisms is currently often performed by comparative evaluation. However, natural variation of plant characteristics between commercial varieties is usually not considered explicitly in the statistical computations underlying the assessment.
  
  
  RESULTS
  Statistical methods are described for the assessment of the difference between a genetically modified (GM) plant variety and a conventional non-GM counterpart, and for the assessment of the equivalence between the GM variety and a group of reference plant varieties which have a history of safe use. It is proposed to present the results of both difference and equivalence testing for all relevant plant characteristics simultaneously in one or a few graphs, as an aid for further interpretation in safety assessment. A procedure is suggested to derive equivalence limits from the observed results for the reference plant varieties using a specific implementation of the linear mixed model. Three different equivalence tests are defined to classify any result in one of four equivalence classes. The performance of the proposed methods is investigated by a simulation study, and the methods are illustrated on compositional data from a field study on maize grain.
  
  
  CONCLUSIONS
  A clear distinction of practical relevance is shown between difference and equivalence testing. The proposed tests are shown to have appropriate performance characteristics by simulation, and the proposed simultaneous graphical representation of results was found to be helpful for the interpretation of results from a practical field trial data set.
authors.affiliation: Wageningen University and Research centre, Biometris, P,O, Box 100, NL-6700 AC Wageningen, Netherlands. hilko.vandervoet@wur.nl
authors.forename: Hilko
authors.initials: H
authors.lastname: van der Voet
authors.forename: Joe N
authors.initials: JN
authors.lastname: Perry
authors.forename: Billy
authors.initials: B
authors.lastname: Amzal
authors.forename: Claudia
authors.initials: C
authors.lastname: Paoletti
mesh_terms: D003627:Data Interpretation, Statistical; D008432:Mathematical Computing; D030821:Plants, Genetically Modified / Q000737:chemistry* / Q000235:genetics; D003313:Zea mays / Q000737:chemistry* / Q000235:genetics