Suppose that you wanted to know if the "favorability rating" of the Mayor of St.Louis
Was still at 65 percent when this survey question was asked three months ago.If the sample size of your study is to be 200 registered voters,what is the approximate value of the standard error of the proportion for these data?
A)0.001
B)0.534
C)0.005
D)0.034
E)0.386

Question

Quizplus · Accepted Answer

We can use the formula for standard error of proportion:
SE = sqrt[p(1-p)/n]
where p is the proportion, 1-p is the complement of the proportion, and n is the sample size.

Since we don't know the current proportion, we can use the proportion from three months ago as an estimate, which is 0.65 (65%). Therefore:
SE = sqrt[0.65(1-0.65)/200] = 0.034

So the approximate value of the standard error of the proportion is 0.034. The answer is (D).

Suppose That You Wanted to Know If the "Favorability Rating