The one-way ANOVA presented in the Lesson is a simple case. In practice, research questions are rarely this “simple.” ANOVA models become increasingly complex very quickly.
The two-way ANOVA model is briefly introduced here to give you an idea of what to expect in practice. Even two-way ANOVA can be too “simple” for practice.
In two-way ANOVA, there are two factors of interest. When there are two factors, the experimental units get a combination of treatments.
Suppose a researcher is interested in examining how different fertilizers affect the growth of plants. However, the researcher is also interested in the growth of different species of plant. Species is the second factor, making this a two-factor experiment. But... those of you with green thumbs say sometimes different fertilizers are more effective on different species of plants!