LMS method
REGRESSION
A total sample size of 492 level-1 units (individuals), which were obtained by sampling 3 level-2 units (PHD) in the control group, 3 level-2 units (PHD) in I only group, 3 level-2 units (PHD) in the E only group, and 3 level-2 units (PHD) in the E+I group, with an average of 41 level-1 units (individuals) per level-2 unit (PHD), achieve >85% power to detect an interaction difference among the group means of at least 3.75. A test based on a mixed-model regression analysis at a significance level of 0.05.