Sample size
The optimum size of the sample was determined using the difference in means between the baseline and post-treatment Symbol Check accuracy scores, which were 0.26 in group A1, 0.08 in group A2, 0.2 in group B1, and 0.05 in group B2, according to the preliminary experiment. Furthermore, it was also calculated based on the differences in the standard deviations of Symbol Check accuracy scores, which were 0.27 in group A1, 0.28 in group A2, 0.29 in group B1, and 0.29 in group B2, according to the preliminary experiment. The overall number of participants was calculated using power analysis in PASS 15.0. This showed that for 80% power at a two-tailed level of significance of 0.05, each group should contain 37 participants for the four-week treatment period. This included an estimated withdrawal rate of 10%. Thus, a minimum of 148 participants (1:1:1:1 randomization ratio) was required.