T-TEST-ONE-SAMPLE (DATA TAILS &OPTIONAL (H0-MEAN 0) &KEY START END KEY)
Returns the t-statistic for the mean of the data, which should be a sequence of numbers. Let D be the sample mean. The null hypothesis is that D equals the `H0-mean.' The alternative hypothesis is specified by `tails': `:both' means D /= H0-mean, `:positive' means D > H0-mean, and `:negative' means D < H0-mean. The function also returns the significance, the standard error, and the degrees of freedom. Signals `zero-variance' if that condition occurs. Signals `insufficient-data' unless there are at least two elements in the sample.