tests were carried out using Bonferroni correction for multiple comparisons.
In experiment 2, the number of migraine attacks, pain intensity,
duration of each attack and painkiller intake were calculated for each
patient before, during and after tDCS sessions. Because we had a small
number of patients in both groups, for migraine severity and frequency
analysis, the effect over time of tDCS sessions was evaluated using
Friedman test. Post hoc analysis with Wilcoxon signed-rank test was
conducted. The differences between groups were analyzed using the
Mann–Whitney test. The strength or magnitude of our results was
determined by calculating the effect size d. According to Cohen [28],
d = 0.2 is a small treatment effect, d = 0.5 represents a moderate effect,
and d = 0.8 is a large effect. The significance level was set at α = 5%.
Analysis was performed using SPSS (Statistical Package for Social
Sciences) version 18.0 for windows (SPSS Inc, Chicago IL, USA).