In a survey of 1002 people, 701 said that they voted in a recent presidential election (based on data from ICR Research Group). Voting records show that 61% of eligible voters actually did vote.
(a) Find a 99% confidence interval estimate of the proportion of
people who say that they voted.
(b) Are the survey results consistent with the actual voter turnout of 61%? Why or why not?
a) = 701/1002 = 0.6996
At 99% confidence interval the critical value is z* = 2.575
The 99% confidence interval for population proportion is
+/- z* * sqrt((1 - )/n)
= 0.6996 +/- 2.575 * sqrt(0.6996 * (1 - 0.6996)/1002)
= 0.6996 +/- 0.0373
= 0.6623, 0.7369
b) since 0.61 doesn't lie in confidence the interval, so the results are not consistent with the actual voter turnout of 61%.
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