Of the roughly 41 million Americans who lacked health insurance for all of 2001, nearly 18 million had moderate-to-high incomes, according to a report highlighting the diversity of the nation’s uninsured population.

More than 14 million Americans were eligible for public insurance programs such as Medicaid and the Children’s Health Insurance Program, but were not enrolled, indicates the study by the National Institute for Health Care Management Foundation.

Another 9 million uninsured were low-income Americans who were not eligible for public programs. For this group, affordability was the biggest hurdle, the study notes.

The research, funded by the Robert Wood Johnson Foundation, found successful initiatives to get coverage for the uninsured were characterized by aggressive marketing to the target population, affordable coverage choices and flexible product design.

The report, “The Uninsured: A Study of Health Plan Initiatives and the Lessons Learned,” can be found online.