Question

Mr. Maria Wilson is considering running for mayor in Rear Gulch, Montana.  Before completing petitions, she decides to conduct a survey of voters. A sample of 500 voters revealed that 400 would support her.

Estimate the value of the population proportion, π.

Determine a 95% confidence interval for the population parameter, π.

Answer 1

Sample proportion, p = 400/500 = 0.8

Estimated value of population proportion, = 0.8

Confidence interval, CI = p Z*

For 95% confidence level, Z* = 1.96

n = 500

CI = 0.8 1.96 x

= 0.8 0.035

= 0.8-0.035 < < 0.8+0.035

= 0.765 < < 0.835