00:01
We have a psychologist who's conducting a study on the effects of a new therapy.
00:08
And so she collected a sample of 20 participants and looked at their data before and after the therapy and found the average decrease in anxiety scores to be 3 .5, so the mean of the differences.
00:31
Sometimes the notation might be like d -bar.
00:34
We might see it as x -bar sub d, something like that.
00:39
Anyway, the decrease is 3 .5, so it's negative 3 .5.
00:44
And the sample standard deviation of those differences as sub d is 1 .2.
00:51
And we're going to assume that the population standard deviation is unknown, so we don't know what this is.
00:56
So the question is, should the psychologist use the t distribution or the z distribution? and since we don't know population standard deviation, we can't use the z distribution.
01:08
We can still use the t distribution because our sample size here is greater than 30...