I am a bit confused by the title, and am not sure how to best word it. (English is not my native language.) Is it: On any given day, 15% of people have a heada

I am a bit confused by the title, and am not sure how to best word it. (English is not my native language.) Is it: On any given day, 15% of people have a headache? (Could be different people every day, but always 15% of world population.) Or is it: 15% of people have a headache every day? (Each of these people have a headache every day.)