Abstract: Determination of sample size (the number of replications) is a key step in the design of an observational study or randomized experiment. Statistical procedures for this purpose are readily available. Their treatment in textbooks is often somewhat marginal, however, and frequently the focus is on just one particular method of inference (significance test, confidence interval). In this talk, I will provide a unified review of approaches and explain their close interrelationships, emphasizing that all approaches rely on the standard error of the quantity of interest, most often a pairwise difference of two means. The focus is on methods that are easy to compute, even without a computer. The main recommendation based on standard errors is summarized as what may be called the 1-2-3 rule for a difference. This method will also be illustrated using a number of more complex examples from my own research and consulting.

Piepho, H.P., Gabriel, D., Hartung, J., Büchse, A., Grosse, M., Kurz, S., Laidig, F., Michel, V., Proctor, I., Sedlmeier, J.E., Toppel, K., Wittenburg, D. (2022): One, two, three: Portable sample size in agricultural research. Journal of Agricultural Science 160, 459-482. DOI: https://doi.org/10.1017/S0021859622000466.

Biography: Hans-Peter Piepho was appointed Professor of Biostatistics at the University of Hohenheim, Stuttgart, Germany in 2001. He has been working as an applied statistician in agricultural research for more than 30 years. His main interests are related to statistical procedures as needed in plant genetics, plant breeding and cultivar testing. Recent interests include envirotype- and marker-enabled breeding, spatial methods for field trials and experimental design for various applications including two-phase experiments and multi-environment trials. Further areas of interest include network meta-analysis and measure of goodness of fit for generalized linear mixed models.