Question

You wish to estimate the proportion of registered voters who plan to vote for Candidate Cal Q. Later in the upcoming election. To do this, you will take a random sample of all registered voters. A poll last month showed Cal with 70% of the votes. How big a sample do you need for a margin of error of four percentage points and a confidence level of 90%?

Answer 1

We have given,                  
Preliminary estimate for proportion (Known) = 0.7
Margin of error =E=0.04
Level of significance =1-0.90=0.1
Z critical value is (by using Z table) =1.645
Sample size formula is                   


=355.17  

Sample size