In: Statistics and Probability
A research institute poll asked respondents if they felt vulnerable to identity theft. In the poll, n = 990 and x = 538 who said "yes." Use a 95 % confidence level.
Solution :
Given that,
n = 990
x = 538
Point estimate = sample proportion = = x / n = 538/990=0.543
1 - = 1-0.543 =0.457
At 95% confidence level the z is ,
= 1 - 95% = 1 - 0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
Z/2 = Z0.025 = 1.96 ( Using z table )
Margin of error = E = Z/2 * ((( * (1 - )) / n)
= 1.96 (((0.543*0.457) /990 )
E = 0.031
A 95% confidence interval is ,
- E < p < + E
0.543 - 0.031 < p < 0.543+0.031
0.512< p < 0.574
(0.512 , 0.574)