A magazine provided results from a poll of 1000 adults who were asked to identify their favorite pie. Among the
1000 respondents,11% chose chocolate pie, and the margin of error was given as plus or minus±5 percentage points. Given specific sample data, which confidence interval is wider: the 90% confidence interval or the 80% confidence interval? Why is it wider?
Choose the correct answer below.
A. A 90% confidence interval must be wider than an 80% confidence interval in order to be more confident that it captures the true value of the population proportion.
B. An 80% confidence interval must be wider than a 90%confidence interval because it contains100%minus−8080%equals=20% of the true population parameters, while the 90% confidence interval only contains 100%minus−9090%equals=1010% of the true population parameters.
C.An 80% confidence interval must be wider than a 90% confidence interval in order to be more confident that it captures the true value of the population proportion.
D. A 90% confidence interval must be wider than an 80%confidence interval because it contains 90% of the true population parameters, while the 80%confidence interval only contains 80%of the true population parameters.
Solution
Option A Answer 1
Explanation
Theoretically, 100(1 - α) % Confidence Interval for the population proportion, p is:
phat ± MoE, where MoE = Zα/2[√{phat (1 – phat)/n}]
with
Zα/2 is the upper (α/2)% point of N(0, 1),
phat = sample proportion, and
n = sample size.
The width of the confidence interval depends only on MoE which in turn depends on Zα/2 only when other things remain the same.
As confidence level increases, α decreases and as α decreases, Zα/2 increases resulting in wider interval.
Physically, more confidence can be gained only by widening the interval.
DONE
Get Answers For Free
Most questions answered within 1 hours.