In a recent poll, 120 people were asked if they liked dogs, and 18% said they did. Find the margin of error of this poll, at the 95% confidence lev

Question

In a recent poll, 120 people were asked if they liked dogs, and 18% said they did. Find the margin of error of this poll, at the 95% confidence lev

Answer 1

mean + and - z(sd)/sqr(n) where z = z score, sd = standard deviation, n= number of people in the survey

using the empirical rule z=2

0.18 + and - 2(sd)/sqr120 is the 95% confidence interval

0.18 + and -sd/sqr30

(0.18-sd/sqr30, 0.18+sd/sqr30)

or a little more accurately z= 1.96 for a 95% confidence interval, alpha = 0.05

0.18 + and -(1.96)(sd)/2sqr30, if you know the standard deviation

but if you don't know the standard deviation, use the t distribution