ABSTRACT
An important factor to be considered in the design of animal experiments is the variation unrelated to the research purpose in the experiment. In animal experiments there are three main sources of variation: variations between researchers; inherent variations in the animals; variations between the animals and the environment. This chapter discusses three variations and provides some suggestions on how to control them. In addition to the variation in genetic background among animals, a number of other effects, which must be considered in the design of experiments, can also increase the differences among animals. A completely randomized design is one in which each animal has the same probability of being assigned to any treatment group in the study. The cross-over design is used in the animal study in an effort to use the animal as its own control. There are many things in common between animal study design and other biomedical studies.
