Given two paired sets 
and 
of 
measured values, the paired 
-test determines whether they differ from each other in a significant
way under the assumptions that the paired differences are independent and identically
normally distributed.
To apply the test, let
 |  |  |
(1)
|
 |  |  |
(2)
|
then define 
by
 |
(3)
|
This statistic has 
degrees of freedom.
A table of Student's t-distribution confidence intervals can be used to determine the significance level at which two distributions differ.
