t-test-matched (sample1 sample2 &optional (tails both))
Returns the t-statistic for two matched samples, which should be equal-length
sequences of numbers. Let D=mean1-mean2. The null hypothesis is that D=0. The
alternative hypothesis is specified by tails': :both' means D/=0, :positive'<br> means D>0, and :negative' means D<0. Unless you're using :both tails, be
careful what order the two samples are in: it matters!
The function also returns the significance, the standard error, and the degrees
of freedom. Signals standard-error-is-zero' if that condition occurs. Signals<br> insufficient-data' unless there are at least two elements in each sample.