In: Statistics and Probability
p ¯ 1 = 0.86, n 1 = 392, p ¯ 2 = 0.97, n 2 = 289.Construct the 90% confidence interval for the difference between the population proportions.
The pooled sample proportion(P) = ( * n1 + * n2)/(n1 + n2)
= (0.86 * 392 + 0.97 * 289)/(392 + 289)
= 0.9067
At 90% confidence level, the critical value is z0.05 = 1.645
The 90% confidence interval is
() +/- z0.05 * sqrt(P(1 - P)(1/n1 + 1/n2))
= (0.86 - 0.97) +/- 1.645 * sqrt(0.9067 * (1 - 0.9067) * (1/392 + 1/289))
= -0.11 +/- 0.0371
= -0.1471, -0.0729