00:01
Here we consider a survey of 2 ,000 americans aged 60 and over, and of the 2 ,000, 1 ,320 received a flu shot.
00:11
We are asked to construct a 90 % confidence interval for the proportion of all american adults aged 60 and over who received the flu shot.
00:21
When we're estimating a population proportion from a large sample, the confidence interval for the proportion is calculated as the sample proportion plus or minus a critical value, z sub alpha over 2, times the standard error, which is the square root of the sample proportion, times 1 minus the sample proportion, over the sample size.
00:48
So first we need to calculate the sample proportion, and this comes out to 0 .66.
01:02
And also, since we want 90 % confidence, this means that alpha is 1 minus 0 .9, which is 0 .1...