In: Statistics and Probability
A random sample of 283 adult Canadians was taken, and 205 of them said that they always vote in federal general elections. Find a 92% confidence interval for the proportion of adult Canadians who say that they always vote in federal general elections |
Solution:
Given:
n = Number of adult Canadians selected in a random sample
n = 283
x = Number of adult Canadians said that they always vote in federal general elections
x = 205
Thus sample proportion of adult Canadians said that they always vote in federal general elections is:
We have to find a 92% confidence interval for the proportion of adult Canadians who say that they always vote in federal general elections.
Formula:
where
Zc is z critical value for c = 0.92 confidence level.
Find Area = ( 1+c)/2 = ( 1 + 0.92 ) / 2 = 1.92 /2 = 0.9600
Thus look in z table for Area = 0.9600 or its closest area and find corresponding z critical value.
Area 0.9599 is closest to 0.9600 and it corresponds to 1.7 and 0.05
Thus Zc = 1.75
Thus
Thus
( Round final answer to specified number of decimal places)
Thus we are 92% confident that the true value of population proportion of adult Canadians who say that they always vote in federal general elections is between the limits: ( 0.6779 , 0.7709).