In: Statistics and Probability
In a survey of 2901 adults, 1495 say they have started paying bills online in the last year.
Construct a 99% confidence interval for the population proportion. Interpret the results.
A 99% confidence interval for the population proportion is
Solution :
Given that,
n = 2901
x = 1495
Point estimate = sample proportion =
= x / n = 1495/2901=0.515
1 -
= 1-0.515=0.485
At 99% confidence level the z is ,
= 1 - 99% = 1 - 0.99 =
0.01
/ 2 = 0.01 / 2 = 0.005
Z/2
= Z0.005 = 2.576 ( Using z table )
Margin of error = E = Z
/ 2 *
((
* (1 -
)) / n)
= 2.576 (((0.515*0.485)
/ 2901)
= 0.024
A 99% confidence interval is ,
- E < p <
+ E
0.515-0.024 < p < 0.515+0.024
(0.491 , 0.539)