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Problem-Solving and Data AnalysisMediumConclusion from a randomised fertiliser experiment

Problem-Solving and Data Analysis practice question

Researchers randomly assigned 200 tomato plants to two groups. One group received a new fertiliser and the other did not; everything else was kept the same. After eight weeks the fertilised plants were 20 percent taller on average. Which conclusion is best supported?

  1. A. The fertiliser likely caused the extra growth in plants like these.Correct
  2. B. The fertiliser will work on every kind of plant.
  3. C. The unfertilised plants were unhealthy.
  4. D. No conclusion about cause can be drawn from this experiment.

Answer: A. The fertiliser likely caused the extra growth in plants like these.

Random assignment with other conditions equal supports a causal conclusion for this kind of plant.

Why the other answers are wrong

B. The fertiliser will work on every kind of plant.
Only tomato plants were tested.
C. The unfertilised plants were unhealthy.
Nothing suggests the control plants were unhealthy.
D. No conclusion about cause can be drawn from this experiment.
Random assignment is exactly what allows a causal conclusion.

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