Suppose you grow tomato plants in a greenhouse and sell the tomatoes by weight, so the amount of money you make depends on plants producing a large total weight of tomatoes. You want to determine which of two fertilizers will produce a heavier harvest of tomatoes, fertilizer A or fertilizer B. There are two distinct regions in the greenhouse: one on the southern side that gets more light and one on the northern side that gets less light. There is room for 20 tomato plants on the southern side and 20 on the northern side. Assume that all the plants are beefsteak tomato plants.
a. Identify the treatment and response variables.
b. Describe a simple randomized design to test whether fertilizer A is better than fertilizer B.
c. Describe a blocked design to test which fertilizer produces a greater weight of tomatoes, blocking by southern side and northern side of the greenhouse. Explain why creating blocks based on whether plants are on the southern or northern side makes sense.
d. Explain why researchers might prefer a blocked design.