SAT OwlQuestion bank / Evaluating statistical claims: observational studies and experiments
A farmer wants to test whether a new fertilizer increases tomato yield. The farmer has similar garden plots available. Which of the following study designs would best allow the farmer to conclude that the fertilizer causes an increase in yield?
Randomly assign of the plots to receive the fertilizer and the other to receive no fertilizer, then compare yields.
Apply the fertilizer to the plots that get the most sunlight, then compare their yields with the other plots.
Apply the fertilizer to all plots and compare this year's yield with last year's yield.
Let a neighbor choose which plots receive the fertilizer, then compare yields.
Show answer and explanation
Answer: A
To establish cause and effect, the treatment must be randomly assigned so that other factors, such as sunlight or soil quality, are balanced between the groups. Only choice A uses random assignment with a comparison group. Then a difference in yield can be attributed to the fertilizer.
Choice C has no comparison group from the same year, so differences in weather between years could explain any change.
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