00:01
We have a sample of 50 retirees, we have the average number of jobs they held, and the population standard deviation.
00:08
So what information do we have? sample size, n, is 50.
00:14
The population standard deviation, sigma, is 2 .1, and point estimate.
00:22
So that's just x bar.
00:24
It's the mean of your sample.
00:26
So that's 7 .2.
00:28
And we want to get confidence intervals.
00:31
So starting out, this is your point estimate.
00:33
It's the mean of your sample.
00:35
The confidence interval is going to look like this.
00:39
Point estimate, plus or minus margin of error.
00:43
And here the margin of error is going to be calculated by z sigma over root n.
00:54
So n is sample size.
00:57
Sigma is the population standard deviation.
00:59
Sometimes you don't have this, you just have sample standard deviation, and then s goes here instead.
01:05
But if we have population, might as well use it.
01:08
Z comes from the confidence level.
01:11
So first we want 95 % confidence, which is a significance level, alpha of 0 .05, alpha over 2 is 0 .025.
01:24
So if i draw a normal distribution, what we're saying is we're starting from our point estimate, and on a normal distribution, we're going to make sure we include 95 % of values, half either way.
01:40
So 5 % are going to be excluded, and they'll be excluded equally on each side.
01:45
So each side is 2 .5%...