Answer: A
Step-by-step explanation:
Confidence interval for the difference in the two proportions is written as
Difference in sample proportions ± margin of error
Sample proportion, p = x/n
Where x = number of success
n = number of samples
For the first treatment,
x = 35
n1 = 50
p1 = 35/50 = 0.7
For the second treatment,
x = 16
n2 = 40
p2 = 16/40 = 0.4
Margin of error = z√[p1(1 - p1)/n1 + p2(1 - p2)/n2]
To determine the z score, we subtract the confidence level from 100% to get α
α = 1 - 0.99 = 0.01
α/2 = 0.01/2 = 0.005
This is the area in each tail. Since we want the area in the middle, it becomes
1 - 0.005 = 0.995
The z score corresponding to the area on the z table is 2.576. Thus, the z score for 99% confidence level is 2.576
Margin of error = 2.576 × √[0.7(1 - 0.7)/50 + 0.4(1 - 0.4)/40]
= 2.576 × 0.10099504938
= 0.26
Confidence interval = 0.7 - 0.4 ± 0.26
= 0.3 ± 0.26
Option A is correct
