A robust nonparametric test which is an alternative to the paired t-test. This test makes the basic assumption that there is information only in the signs of the differences between paired observations, not in their sizes. Take the paired observations, calculate the differences, and count the number of +s n_+ and -s n_-, where N congruent n_+ + n_- is the sample size. Calculate the binomial coefficient B congruent (N n_+).