Sample size calculation
headache-day reduction
The sample size was determined on the basis of previous experience of the team, hypothesizing that 48% of patients allocated to TaU would achieve ≥ 50% headache-day reduction after 12 months, and that adding mindfulness might increase this figure by 20%. We set alpha at 0.05 and power at 80%, and determined that 75 patients per group were needed; considering that up to 12% of patients might be lost at follow-up, we determined that 170 patients should be randomized. The G-Power software was used for sample size calculation.