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t-test (sample-1 sample-2 &optional (tails both) (h0mean 0))

Returns the t-statistic for the difference in the means of two samples, which

should each be a sequence 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' 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.