10.3.2, population means vs sample means of tutorial groups

[michaeladamkatz]

Okay, so let’s let µ1 denote the true population mean for group 1 (e.g., Anastasia’s students), and µ2 will be the true population mean for group 2 (e.g., Bernadette’s students),7 and as usual we’ll let X¯1 and X¯2 denote the observed sample means for both of these groups.

It confusing me to think about "population" vs. "sample" means in this sentence because as I understand it, the data set we have for the Dr. Harpo's class includes all the students in Anastasia’s tutorial and all the students in Bernadette’s tutorial. So I think this sentence is talking about the more general case where the sample is just a representation, but in the context of this particular example where we have the complete data it's confusing.

Also, on page 226 it says:

In our example, Anastasia’s students had an average grade of 74.533, and Bernadette’s students had an average grade of 69.056, so the difference between the two sample means is 5.478. But of course the difference between population means might be bigger or smaller than this.

But in this case we have all the students that are in the respective tutorials, right? So what does "population" mean?

Well, I guess the population would be the theoretical students who might take each of the two tutorials in future years. Might be good to call this out. I know there is a footnote about this in 10.3.2. It still seems messy.