Let
and
be the observed mean and variance of a sample of
drawn from a normal universe with unknown mean
and let
and
be the observed mean and variance of a sample of
drawn from a normal universe with unknown mean
. Assume the two universes have a common variance
,
and define
(1)
| |||
(2)
| |||
(3)
|
Then
(4)
|
is distributed as Student's t-distribution
with
.