00:01
We need to find a critical value.
00:03
Our sample size is 13.
00:06
Our level of confidence is 85%.
00:08
And we're looking for a t value because we have this small sample.
00:14
So i'll start by drawing a t distribution.
00:17
It looks a lot like the standard normal distribution, except the tails are wider.
00:22
And there are many t distributions based on degrees of freedom.
00:26
The fewer the degrees of freedom, the wider the tails.
00:28
The more degrees of freedom, the closer this gets to a standard normal curve.
00:33
Just like the standard normal curve, the mean is 0, the total area is 1, and it's symmetric.
00:40
So when we say we want the critical value for a confidence level of 85%, that means if i put t and minus t on here, it will contain 85 % of this curve between it, 0 .85.
00:55
So we're looking for t to make that happen.
00:57
Now we need three pieces of information.
01:01
First, that this is two tails.
01:03
Confidence intervals tend to be two tails...