Design and analysis of efficacy evaluation trials

This standard is intended to provide general background information on the design and analysis of efficacy evaluation trials. The EPPO Standards for the efficacy evaluation of plant protection products provide more detailed instructions on such trials for individual host/pest combinations. The set-up of a trial is first considered (experimental design, plot size and layout, role and location of untreated controls). The nature of observations to be made is then reviewed (types of variables, modes of observation). Finally, suggestions are made on the statistical analysis of the results of a trial and of a trial series (estimates of effects, choice of the statistical test, transformation of variables). Appendix 1 gives examples of scales used in the EPPO standards. What follows is intended to give an outline of good statistical practice in the analysis of data. It is not, and cannot be, a prescription for all analyses, and cannot cover all situations. Practitioners should never underestimate the need for professional statistical advice. It is important for practitioners to understand the advice they receive. It is often better for them to perform a simple analysis that they can report and defend with confidence, than to accept advice that leads to an analysis that they may understand only partially. The bibliography at the end of these standards may be helpful. It gives several good texts that attempt to reveal the principles of good statistical practice, rather than to provide a series of statistical recipes to be followed blindly. 1. Experimental design