Question 521:

Asked on November 24, 2008

Tags: Confidence Intervals , Proportion , Confidence Level

1

Answer:

No answer provided yet.

This answer wants you to consider the relationship between the confidence level and width of the confidence interval. All things being equal, the width of a confidence interval will INCREASE as your level of confidence increases. This is because we need to be more confident the mean or proportion fall within the interval. This is demonstrated in the confidence level tutorial.

a is wrong because the interval gets wider not narrower as the confidence level increases.

b is wrong because as your sample size increases your confidence interval width narrows (as we gather a larger sample our confidence in the results increase)

d is incorrect because a confidence interval around a proportion is at its widest when p=.50. You can test this out quickly by using the confidence interval around a proportion calculator and entering 20/100 and 50/100. We see the margin of error is wider at 50/100 (p=.50).

c is the correct answer because the level of confidence is lower and lower confidence levels mean narrower confidence interval widths.