Out of 400 people sampled, 132 had kids.

Question

Out of 400 people sampled, 132 had kids. Based on this, construct a 90% confidence interval for the true population proportion of people with kids. Give your answers as decimals, to three places

Answer 1

phat +/- Z_.05*Sqrt(phat*(1-phat)/n) Z_{.05 =} InvNorm(.05,0,1,RIGHT) =1.645

phat = 132/400 = 0.33

0.33+/-1.645 * sqrt(0.33*0.67/400)

(0.291, 0.369)

We are 90% Confident that the true proportion is between 0.291 and 0.369.