Problem-Solving and Data AnalysisVery hardDesigning a fair comparison
Problem-Solving and Data Analysis practice question
A farmer wants to test whether a new fertiliser increases wheat yield. Which design gives the most reliable comparison?
- A. Divide one field into 20 equal plots, randomly assign 10 to the new fertiliser and 10 to the old, and compare the average yields.Correct
- B. Use the new fertiliser on the field nearest the river and the old on the hill field, and compare.
- C. Use the new fertiliser this year and compare with last year's yield.
- D. Ask neighbouring farmers which fertiliser they prefer.
Answer: A. Divide one field into 20 equal plots, randomly assign 10 to the new fertiliser and 10 to the old, and compare the average yields.
Random assignment within one field controls for soil, water, and weather.
Why the other answers are wrong
- B. Use the new fertiliser on the field nearest the river and the old on the hill field, and compare.
- Different fields differ in soil and water.
- C. Use the new fertiliser this year and compare with last year's yield.
- Different years differ in weather.
- D. Ask neighbouring farmers which fertiliser they prefer.
- Opinions are not a yield measurement.
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