ABSTRACT
The ability to test for the presence of interaction effects is sufficient justification in biology for conducting factorial experiments. In experimental design a particular treatment (independent variable) is referred to as a factor. A factorial experiment is a set of treatments made up of 2 or more factors. Each factor is present in the experiment at 2 or more levels, such that all possible combinations of the levels of the 2 factors are present. Since in biology one should at least consider the possibility of interaction among factors, the single factor study is generally inadequate. The factorial experiment, by including independent combinations of the levels of all factors, permits the researcher to test hypotheses concerning interaction effects. In biology, the testing and interpretation of interactions is likely to be of the greatest importance.
