Example: Five seeding rates and one cultivar.
A factorial is not a design but an arrangement.
A factorial is a study with two or more factors in combination.
Each level of a factor must appear in combination with all levels of the other factors.
Factorial arrangements allow us to study the interaction between two or more factors.
Interaction:
1. the failure for the response of treatments of a factor to be the same for each level of another factor.
2. When the simple effects of a factor differ by more than can be attributed to chance, the differential response is called an interaction.