00:01
We're going to get two confidence intervals about a sample mean to find the true average or its frequency for all tense records and we're testing for the population.
00:15
So we're going to find the value of the sample mean residence frequency and we're going to do that by taking the average of the confidence intervals.
00:25
So what i mean by that is here's our interval on the number line here and we have a lower value here and the upper value here and the confidence intervals are symmetric so the mean is right between the lower and the upper bound so we just take the average of these values so you add them up divided by two and we end up with 114 .7s or both of them it's kind of nice now which of these is the 90 % and which of these is the 99 well let's look at the width of the interval that's going to tell us so the difference between these two values is 1 .2 and the difference between these is 1 .8.
01:08
So this one here, this 113 .8 to 115 .6, this is our 90, excuse me, our 90 % confidence interval.
01:21
No, sorry, 99.
01:25
And this one, the 114 .1 up to 115 .3, this is our 90 % confidence.
01:34
Because the way we get more confidence is we make our interval wider to ensure that we're capturing that true population.
01:40
So that's why this.
01:41
This one here, which i have on the right, so 13 .8 is the 99 % because it's a wider interval versus the general.
02:00
It's a shorter interval.
02:03
There we can tell because the 99 % confidence interval should be wider.
02:12
So the center is the same, because it's based on the same sample statistics.
02:20
All right, so now we're going to make a competence interval and we're told, we're given a head.
02:24
Headline that 30, 35%, as i was reading that headline, i noticed i made a mistake.
02:35
This is the, i got 36 instead of 35, so there's our values right there.
02:41
So we're told that 35 % of people on high risk coast will refuse evacuation orders, and they sampled 6 ,640 adults.
02:54
And we're making a 98 % confidence interval, and the formula is given as a this is a population about portion, so it's p hat plus minus z alpha over two times the square root of p hat plus one minus p hat all over n.
03:29
So we have all these parameters.
03:31
P is the percentage, the 0 .35.
03:35
N is 6640.
03:37
So we get our formula, that's one of the .35, that's the one thing we need...