Question

What does this notation mean? (confidence intervals)

Answer 1

this is a t-statistic right?

Answer 2

from what I'm reading it appears that the subscript 0.01 is a probability, while the (20) represents the "degrees of freedom." I'm not entirely familiar with these concepts, but maybe these links will make more sense to you:

http://go.owu.edu/~deswartz/210/text_notes/ch09.htm
http://www.math.ku.edu/ksacg/728/2013_Sp/homework_solns/728HW2_Dean.pdf

Answer 3

Yes it is and thank you.