Over 600 million people aged 18–65 will have headache tomorrow: global 1-day prevalence and recall bias from a meta-analysis of individual participant data (N = 38,512) from the general populations of 15 countries

BACKGROUND: Our recent estimate of the global 1-year prevalence of headache among those aged 18-65 years was 65%: considerably higher than previous estimates, but based solely on high-quality epidemiological data derived from a large population-based sample. Here we present complementary estimates of 1-day prevalence. METHODS: We performed a meta-analysis of individual participant data from cross-sectional surveys among population-representative samples (age range 18-65 years) from 15 countries and all world regions. All used the Headache-Attributed Restriction, Disability, Social Handicap and Impaired Participation (HARDSHIP) questionnaire, including the question "did you have a headache yesterday?", from which 1-day prevalence was determined. An algorithmic process applying modified ICHD criteria yielded separate estimates for migraine, tension-type headache (TTH) and probable medication-overuse headache (pMOH: the association of headache on ≥ 15 days/month and medication overuse). We analysed associations with age, gender and country-income level, and adjusted prevalence estimates for these factors. We calculated predicted 1-day prevalence from 1-year prevalence and reported headache frequency. RESULTS: Among the 38,512 participants, females (53.4%) and participants from low- (17.1%) or lower-middle-income countries (64.6%) were overrepresented, but age distribution fairly matched that of the world. Overall, 13.7% (95% CI: 13.3-14.0) reported headache yesterday, females (17.1% [16.6-17.6]) more than males (9.7% [9.3-10.2]). Migraine was the most common headache type yesterday (6.0% [5.8-6.3]), followed by TTH (4.1% [3.9-4.3]) and pMOH (2.3% [2.2-2.5]). One-day headache prevalence was higher in low/lower-middle-income countries (13.9% [13.6-14.3]) than in high/upper-middle-income countries (12.4% [11.6-13.2]). Predicted 1-day prevalence (10.9% [10.7-11.1]) was considerably lower than observed 1-day prevalence (13.7% [13.3-14.0]), although not among those with pMOH (3.1% [3.0-3.3] versus 2.3% [2.2-2.5]). Adjusted for age, gender and country-income level, global 1-day prevalence estimates were 13.1% (12.8-13.5) for any headache, 5.7% (5.5-5.9) for migraine, 3.9% (3.7-4.1) for TTH and 2.4% (2.3-2.6) for pMOH, with 1.0% undiagnosed. CONCLUSION: Assuming yesterday was no different from any other day, an estimated 13.1% (N = 641,900,000) of the world's population aged 18-65 years will have headache tomorrow; almost half will be migraine. People with migraine or TTH underestimate the frequency of headache episodes. Since headache-attributed burden is usually estimated from recalled frequency over 1-12 months, this also may be underestimated.