Introduction

Many of the fundamental ideas and principles of experimental design were developed by Sir R. A. Fisher at the Rothamsted Experimental Station (Fisher, 1926). This agricultural background is reflected in some terminology of experimental design that is still being used today. Agricultural experiments are conducted, e.g., to compare different varieties of a certain crop or different fertilizers. In general, those that are under comparison in an experiment are called treatments. Manufacturing processes in industrial experiments and drugs in pharmaceutical studies are examples of treatments. In an agricultural experiment, the varieties or fertilizers are assigned to plots, and the yields are compared after harvesting. Each plot is called an experimental unit (or unit). In general, an experimental unit can be defined as the smallest division of the experimental material such that different units may receive different treatments (Cox, 1958, p. 2). At the design stage, a treatment is chosen for each experimental unit.