A hypothesis test for the mean of the pairwise difference (or the mean difference of the pairs) of two groups. It tests the null hypothesis
H0: mued = delta 0
where the hypothesised difference is almost always 0, using the statistic
t= ((bar d) - delta 0)/ SE(d)
with n-1 degrees of freedom where the SE((bar)d)= sd/(root)n and n is the number of pairs.