A survey of 350 union members in New York State reveals that 63% favor the Republican candidate for governor
a) Construct a 90% confidence interval for the true proportion of all New York State union members who favor the Republican candidate. Round the limits to 3 decimal places.
b) Interpret the interval.
Solution :
Given that,
Point estimate = sample proportion = = 0.63
1 - = 0.37
Z/2 = 1.645
Margin of error = E = Z / 2 * (( * (1 - )) / n)
= 1.645 * (((0.63 * 0.37) / 350)
= 0.042
a) A 90% confidence interval for population proportion p is ,
- E < p < + E
0.63 - 0.042 < p < 0.63 + 0.042
0.588 < p < 0.672
b) We are 90% confidence that interval for the population proportion p is between 0.588 and 0.672
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