A univariate halting test using the Wilcoxon test, which must be satisfied for all condition pairs.
U_halt(condition, covariates, thresh)
The ratio of the p-value and the threshold, or 0 if the p-value is less than the threshold. If there are more than two conditions, it returns the smallest value found for any condition pair.
A factor vector containing condition labels.
A columnwise matrix containing covariates to match the conditions on.
The return value of halting_test has to be greater than or equal to thresh for the matched groups.