SAT Math · Evaluating statistical claims: observational studies and experiments · medium
A researcher wants to test whether a new fertilizer increases plant growth. Instead of using two separate groups of different plants, the…
A researcher wants to test whether a new fertilizer increases plant growth. Instead of using two separate groups of different plants, the researcher splits each individual plant's root system into two pots, one receiving the new fertilizer and one receiving a standard fertilizer, and compares growth within each pair. What is the main advantage of this matched-pairs design?
Answer and explanation
Answer: B: It reduces the effect of natural variation between different plants, since each comparison is made within a genetically identical pair.
In a matched-pairs design, each plant receives both treatments, one on each half of its roots. Comparisons are then made within the same plant, so differences in genetics, size, and health between plants cancel out. This reduces variation unrelated to the fertilizer and makes the comparison more precise, which is choice B. Choice A is not an advantage, because splitting each plant does not necessarily increase the number of plants. Choice C is wrong, since a comparison condition (the standard fertilizer) is still needed. Choice D overstates what any design can do, because no design can guarantee a significant result.
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