Two samples are taken with the following numbers of successes and sample sizes

Question

Tow samples are taken with the following numbers of successes and sample sizes

r1 = 40r2 = 32

n1 = 69n2 = 85

Find a 91% confidence interval, round answers to the nearest thousandth.

___ < p1 - p2 < ___

Answer 1

Compute the sample proportions:

p1 = r1/n1

p2 = r2/n2

Determine the z-critical for 91% CI. Look up z-score corresponding to 95.5 percentile. That is your z-critical.

compute the standard error estimate (SE):

sqrt(p1 *(1-p1)/n1 + p2(1-p2)/n2)

CI = p1 - p2 +/- z-critical * SE