Multiple Choice: What is the design for this experiment?
The prompt is the following: A biology student wants to determine if using a fertilizer would help promote the growth of new babies in spider plants. The student has access to 90 baby spider plants of three varieties: green, variegated, and curly. There are 30 plants of each variety. They all are potted in the same amount and type of soil, given the same amount of water, and exposed to the same amount of light. The numbers 1–30 are written on slips of paper, placed in a hat, and mixed thoroughly. A plant is selected and a slip of paper is drawn. If the slip has the numbers 1–15, then the plant will receive fertilizer. If the slip has the numbers 16–30, the plant will not receive fertilizer. A green spider plant is selected and a slip of paper is drawn. This plant is placed in the treatment group indicated by the number, and the slip is not put back in the bag. The slips are mixed again, the next green spider plant is selected, and a slip is drawn. The plant is placed in the treatment group indicated by the number. This procedure is repeated until all 30 green spider plants are assigned to treatments. The numbered slips are placed back in the bag and this procedure is repeated for the remaining types of spider plants. After one year, the shoots will be counted for each plant.
The answer choices are as follows:
A. observational study
B. matched pairs design
C. randomized block design
D. completely randomized design
My solution: My guess is C. In this case, the matched pair is when each experimental unit receives both treatments in random order, and the participants were separated into the yoga or meditation group by a flip of the coin. In A, I do not think that it is a matched pair because each person was asked their stress level. I rule out D as well, because I do think this is a matched pairs design.