Estimating the Difference between Two Population Proportions
Question 8 • CA-Statistics and Probability B
In the study on a drug for lowering cholesterol levels, after 1 month:41 of 55 subjects reduced cholesterol with new medicine.34 of 50 subjects reduced cholesterol with old medicine.99% confidence interval: (–0.163, 0.293)Choose the correct conclusion.
Answer
A
We are 99% confident that the interval from -0.163 to 0.293 captures p1 – p2, the difference in the sample proportions of patients like these who would have their cholesterol lowered as a result of using the new drug versus using the old drug.
B
We are 99% confident that the interval from -0.163 to 0.293 captures p1 – p2, the difference in the true proportions of patients like these who lowered their cholesterol as a result of using the new drug versus using the old drug.
C
We are 99% confident that the interval from -0.163 to 0.293 captures p1 – p2, the difference in the true proportions of patients like these who would have their cholesterol lowered by using the new drug versus using the old drug.
D
We are 99% confident that the interval from -0.163 to 0.293 captures p1 – p2, the difference in the true means of patients like these who would have their cholesterol lowered by using the new drug versus using the old drug.
Explanation
The interval estimates p1 − p2, the difference between the true proportions of similar patients whose cholesterol would be lowered by the new drug and by the old drug. Choice C describes that population difference. Choice A incorrectly refers to sample proportions, and choice D refers to means; the outcome is categorical (lowered or not).
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