Prevalence Calculation for Migraine Headaches
The prevalence of migraine headaches among these clinic patients is 37.5% (75 out of 200 patients). This is calculated by dividing the number of patients with migraine (75) by the total number of patients assessed (200), then multiplying by 100.
Understanding the Calculation
- Point prevalence = (Number of existing cases / Total population at risk) × 100
- In this scenario: (75 / 200) × 100 = 37.5%
The population figure of 100,000 mentioned in the question is not relevant to calculating the prevalence among the 200 clinic patients actually assessed. Prevalence is specific to the defined population being studied—in this case, the 200 adult patients attending the clinic on that particular day.
Clinical Context of This Finding
This 37.5% prevalence is substantially higher than expected population-based estimates. According to recent U.S. data, migraine affects approximately 16% of the general adult population, with 21% of females and 11% of males affected 1. More recent surveillance data from 2015 shows a 3-month prevalence of 15.3% overall (20.7% in females, 9.7% in males) 2.
The elevated prevalence in this clinic sample (37.5% vs. 16% in the general population) likely reflects selection bias, as patients attending a clinic are more likely to have active health concerns, including migraine 3, 2.
Important Considerations
- This represents a clinic-based sample, not a population-based estimate, which explains the higher prevalence compared to general population surveys 3, 2
- The 3-month prevalence in the general U.S. population has remained stable over nearly two decades, ranging from 14.9% to 15.3% 3, 2
- Migraine prevalence is highest in adults aged 18-44 years (17.9-23.5%), females, unemployed individuals, and those with household income less than $35,000 annually 1, 3, 2
- Migraine remains underdiagnosed and undertreated, with studies showing that 82% of patients with a clinic diagnosis of "nonmigraine headache" actually had IHS-defined migraine or probable migraine when assessed longitudinally 4