00:01
All right, so we've got a test here with 42 subjects.
00:06
We have a mean of 5 .5 and a standard deviation of 17 .6.
00:10
We want to construct a 90 % confidence interval.
00:13
So since we have more than 30 subjects, this is considered a large study.
00:18
So we use the formula, x bar plus minus z times the standard deviation over square rate of n.
00:28
All these numbers are given to you.
00:29
Let's break that down.
00:30
X bar is the mean 5 .5.
00:35
Standard deviation right here is 17 .6.
00:40
Your end value, well, that's 42.
00:43
And the z value, well, that's given to you anyways, like in a table.
00:47
And we want to do a 90 % confidence interval.
00:49
So our z value here, we want 0 .645.
00:54
The plus minus here, that means you go through once with this just a plus, and then once with just a minus.
01:01
So there's two form it's like there's two different values in there.
01:06
So first off we'll do the plus so 5 .5 plus that z value of 1 .645 standard deviation 17 .6 square way to n in was 42 go through it once with a plus and once with a minus we get two values so 5 .5 plus 1 .645 parentheses 17 .6 divided by the square root 42.
01:50
We're going to wind up with 9 .97.
01:54
We'll do it again with a negative in there, with a minus.
02:04
And we get a 1 .03.
02:08
1 .03.
02:10
So our confidence interval says that we are 90 % confident that the estimated mean net change would be between 1 .03 and 9 .97.
02:28
So what does, so we've got that part figured out.
02:33
What's the confidence interval? so what does that confidence interval suggest about the effectiveness of the treatment? well, it does not contain zero.
02:45
So we don't contain zero here.
02:47
There's not a zero in between there.
02:48
Zero's down here, zero, one...