Comparing prospective headache diary and retrospective four-week headache questionnaire over 20 weeks: Secondary data analysis from a randomized controlled trial.

Over time, the concordance between headache days reported in these two measures tended to increase; however, the recall questionnaire headache estimates were lower than the diary measures in all four periods. When analysis was restricted to headaches lasting 8 hours or more, the number of headache days was more closely aligned with days reported in the recall questionnaire, indicating that the accuracy of recall estimates is likely to be influenced by headache duration. Restriction of analyses to moderate-to-severe headaches did not change results as much as headache duration. The findings indicate that recall questionnaires administered on a monthly basis may underestimate headache frequency and therefore should not be used interchangeably with headache diaries.Clinical Trials.gov Identifier: NCT02012790.