Permutation test based on Pearson's linear correlation coefficient (r) or Spearman's rank correlation coefficient (rho). This function can perform the test on one or more pairs of variables. When applying the test to multiple pairs of variables, the "max statistic" method is used for adjusting the p-values of each variable for multiple comparisons (Groppe, Urbach, & Kutas, 2011). Like Bonferroni correction, this method adjusts p-values in a way that 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.