Tjen-Sien Lim asks:
> Why are people so obsessed with T and Z? When the degrees of freedom
exceeds
> say 30, the difference between T and Z is practically negligible. You can
use T
> or Z in such a case. However, the P-value from Z is easier to compute.
With appropriate tables or software, the P-value from Z is *not* any
easier to compute.
I don't think most of us here are "obsessed with T and Z" but, rather,
concerned by others' obsession with it. I see it as a needless confusion
and a waste of time. Moreover, it has been observed that the meme tends to
mutate in the wild from harmless superstition ("I should use Z when n>30")
to actual error ("Anybody who uses t with n>30 is wrong.")
*Instructors* should consider this as a pedagogical matter; the question
should ideally never arise in the classroom. Unfortunately, many textbooks
and instructors in other courses sow the seeds of this silly little
anachronism, and it may be necessary to weed them out.
-Robert Dawson
