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 a help 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.
A clear distinction of practical relevance is shown between difference and equivalence testing. The proposed procedure of simultaneous testing is shown to have appropriate performance characteristics by simulation, and the proposed graphical representation of results was found to be helpful for the interpretation of results from a practical field trial data set.
The article is published online within the journal, BMC Biotechnology and is free to access.