sentence: About 7.68% of total migraine cases are chronic migraines and about 1% of people in the United States have CM, with a higher rate among females, middle-aged people, and in those households that had the lowest annual income.
modified: fix grammar: About 7.68% of total migraine cases is chronic migraines and about 1% of people in the United States has CM, with a higher rate among females, middle-aged people, and in those households that had the lowest annual income.