Additional Principles of Experimental Design — Quiz
Question 5 • Statistics and Probability
A biology student wanted to determine if using fertilizer would promote plant growth. One hundred plants were randomly assigned to one of two groups: one that received fertilizer, and one that did not receive fertilizer. Which of the following statements is true about the benefits of random assignment?
Answer
A
The variability between each plant may not be evenly distributed between the two groups, so any observed differences in the plant growth between the two groups may or may not be due to the fertilizer.
B
The variability between each plant would be evenly distributed between the two groups, so any observed differences in the plant growth between the two groups are more likely due to the fertilizer.
C
The variability between each plant may not be evenly distributed between the two groups, so any observed differences in the plant growth between the two groups would not be due to the fertilizer.
D
The variability between each plant would be evenly distributed between the two groups, so any observed differences in the plant growth between the two groups are guaranteed to be due to the fertilizer.
Explanation
Random assignment tends to balance natural differences among plants, such as starting size or health, across the fertilizer and no-fertilizer groups. This makes it more likely that a difference in growth between the groups is caused by the fertilizer rather than by preexisting differences. Random assignment does not guarantee perfectly equal variability, so D is too strong; B is the best choice.
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