In: Statistics and Probability
A 95% confidence interval for a difference in proportions p1-p2 if the samples have n1=60 with p^1=0.69 and n2=60 with p^2=0.56, and the standard error is SE=0.09.
Solution:
Point estimate of difference between two proportions
= 1 - 2
= 0.69 - 0.56
= 0.13
Our aim is to construct 95% confidence interval.
c = 0.95
= 1- c = 1- 0.95 = 0.05
/2 = 0.025
= 1.96 (use z table)
Margin of error = * =
= 1.96 * 0.09
= 0.1764
Required interval is
Point estimate Margin of error
0.13 0.1764
(0.13 - 0.1764 , 0.13 + 0.1764)
(-0.0464, 0.3064)
Required 95% confidence interval is (-0.0464, 0.3064)