On a regular spring time a lot of tulip flower fields outside the Keukenhof are headed (taking the flower off) on the 30th of April or within a couple of days after it. If you want to see the flower fields as well make sure that you visit before this date!
In factorial designs, a factor is a major independent variable. In this example we have two factors: time in instruction and setting. A level is a subdivision of a factor. In this example, time in instruction has two levels and setting has two levels. Sometimes we depict a factorial design with a numbering notation.
The interaction between two factors can be calculated in the same fashion. First, the design matrix must be amended to show the high and low levels of the interaction. The levels are calculated by multiplying the coded levels for the input factors acting in the interaction.