summarize the results of the hypothesis test
if use_t is True, then t test results are returned if use_t is False, then z test results are returned
significance level for the confidence interval, coverage is
str, ‘pooled’ or ‘unequal’
pooled, then the standard deviation of the samples is assumed to be the same. If
unequal, then the variance of Welch ttest will be used, and the degrees of freedom are those of Satterthwaite if
difference between the means under the Null hypothesis.