Question

The 98 percent confidence interval (−0.248,−0.134) was constructed to estimate the slope of a regression model for a bivariate data set with 20 values. Alice claims that a sample size of 25 will produce a narrower interval, all other things remaining the same. Desmond claims that a sample size of 15 will produce a narrower interval. Which statement is true about the claims made by Alice and Desmond?

a. Alice’s claim is correct.
b. Desmond’s claim is correct.
c. Both Alice’s claim and Desmond’s claim are correct.
d. Neither Alice’s claim nor Desmond’s claim is correct.
e. There is not enough information to determine whether the claims are correct.

Answer 1

a. Alice’s claim is correct.

Explanation:

Margin of error of a confidence interval:

The margin of error of a confidence interval is inversely proportional to the sample size. This means that a smaller sample size leads to a smaller margin of error and a narrower interval, while a larger sample size leads to a larger margin of error and a wider interval.

Alice claims that a sample size of 25 will produce a narrower interval

25 > 20, so smaller margin of error and narrower interval, which means that Alice is correct.

Desmond claims that a sample size of 15 will produce a narrower interval.

15 < 20, so larger margin of error and wider interval, which means that Desmond is wrong.

So the correct answer is given by option a.