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.
Main concerns in experimental design include the establishment of validity, reliability, and replicability. For example, these concerns can be partially addressed by carefully choosing the predictor, reducing the risk of measurement error, and ensuring that the documentation of the method is sufficiently detailed.