REML and the analysis of series of variety trials

• Main Author: Nabugoomu, Fabian
• Published: University of Edinburgh 1994
• Subjects: 519
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659844

In the UK, official series of trials are grown annually at several centres with the objective of predicting future variety performance under the growing conditions sampled by the trials. For this purpose, the centres are chosen to be representative of the growing conditions in the region to which results will be applied. Analysis involves combination of trial results over centres and years. The analysis for individual years is also important as it predicts performance under conditions of a particular year and is also required for monitoring the trials. Varieties x environments tables are inevitably incomplete and the use of interactions as error makes the REML algorithm suitable for analysis. The models for analysis are determined solely by the objectives of analysis and the data structure. To predict variety performance for a range of conditions sampled by the trials, only variety effects should contribute to the systematic part of the model, all other effects and interactions are error. In this thesis we use REML to analyse the varieties x centres x years table, varieties x years/centres table and the varieties x regions/centres x years table. Simple methods based on least-squares analysis of two-way tables have been used to provide a combined analysis. We show that these methods give the same means as a full analysis if the within years tables are complete. Moreover, if centres are nested within years, use of REML in a two-stage analysis also gives correct standard errors. If some or all within-years tables are incomplete, simple methods can be inefficient.