The HDI was designed to assess the burden of headache using 25 items that inquire about the perceived impact of headache on emotional functioning (eg, “Because of my headaches I feel handicapped”) and daily activities (eg, “Because of my headaches I feel restricted in performing my routine daily activities”). Possible answers for each item are YES (2 points), SOMETIMES (1 point) and NO (0 points). Thirteen items asses the emotional component of headache (maximum score: 36) whereas the remaining 12 items assess the physical component (maximum score: 24). A greater score suggests a greater burden of headache. The HDI has exhibited good test–retest reliability at short ( r = 0.93-0.05) and long-term ( r = 0.76-0.83)