1 Gallup tracks daily the percentage of Americans who approv

1. Gallup tracks daily the percentage of Americans who approve or disapprove of the job Barack Obama is doing as president. Daily results are based on telephone interviews with approximately 1,500 national adults; Margin of error is ±3 percentage points. What is the confidence level used in Gallup’s polls?

Solution

Compute Sample Size ( n ) = n=(Z/E)^2*p*(1-p)
Z a/2 at 0.0201 is = 2.324
Samle Proportion = 0.5
ME = 0.03
n = ( 2.324 / 0.03 )^2 * 0.5*0.5
= 1500.2711 ~ 1501

I Experimented this with 98% C.I & it is 2.324

Apprixmately it 98% confidence level