Independent sample permutation test based one of three t-statistics (equal variance, Welch's t, t_dif). This function can perform the test on one variable or simultaneously on multiple variables. When applying the test to multiple variables, the "tmax" method is used for adjusting the p-values of each variable for multiple comparisons (Blair & Karnisky, 1993; Westfall & Young, 1993). Like Bonferroni correction, this method adjusts p-values in a way that strongly controls the family-wise error rate. However, the permutation method will be more powerful than Bonferroni correction when different variables in the test are correlated.