Design of sensory multi-session trials with preparation constraints

Design of sensory multi-session trials with preparation constraints Designs for sensory studies must satisfy several requirements. Usually a given number of products are to be evaluated and there is an upper limit to the number of assessors available. Due to variation in sensory perception, inter-assessor product comparisons are preferred. For large product numbers, trials are split into sessions to avoid sensory fatigue and the sequential presentation of products can cause order and carry-over effects. Thus, resolvable row-column or cross-over designs are required, which ensure that each assessor tastes all products the same number of times. In this thesis a three-step procedure is proposed to generate designs for trials where the number of products prepared for or served in each session is limited. First, an incomplete block design with a special column structure, the preparation design, is created, assigning products to sessions. Secondly, a cross-over design is constructed, assigning the columns of the preparation design to assessors. In the third step the two designs are combined by identifying the column-order of the preparation design that results in the highest average efficiency of the complete cross-over design. Search algorithms for incomplete block and cross-over designs are modified to produce preparation and panel designs with a special structure to guarantee resolvability of the complete sensory design. This procedure has been enhanced to produce designs for trials involving a control and several test products, in which control-test comparisons are estimated with higher precision than test-test comparisons. Two distinct construction methods have been developed for this case. By using factorial preparation designs the three step procedure can also be adapted for creating factorial multi-session designs with or without a control product

Crop-to-crop gene flow using farm scale sites of oilseed rape (Brassica napus) in the UK

From 2000-2003 a range of Farm Scale Evaluation (FSE) trials were established in the UK to assess the effect of the release and management of herbicide tolerant (HT) crops on the abundance and diversity of farmland wildlife compared with their conventionally managed non-GM-equivalents. The objective of this research project was to investigate gene flow within the winter (WOSR) and spring oilseed rape (SOSR) FSE trials and to develop a statistical model for the prediction of cross-pollination frequency that can be used to evaluate current separation distance guidelines. Seed samples were collected from the non-GM half of the trial sites and were tested for evidence of cross-pollination from the GM HT halves using a quantitative PCR assay specific to the HT (bar) gene. Rates of cross-pollination were found to decrease rapidly with increasing distance from the GM source. The quantitative data were subjected to statistical analysis and a two-step model was found to provide the best fit for the data. Significant differences were found between the results for WOSR, SOSR and varietal association (VA) crops. The model predicted that the %GM content (including upper 95% confidence limits) of a sample taken at a distance of 50 m away from the GM source would be 0.04% (0.84%) for WOSR, 0.02% (0.39%) for SOSR, 0.77% (21.72%) for WOSR VA and 0.37% (5.18%) for SOSR VA. The data and models presented here are discussed in the context of necessary separation distances to meet various possible thresholds for adventitious presence of GM in OSR