Most Americans with health insurance have some form of group coverage — through employer-sponsored plans, government programs such as Medicaid or Medicare, military programs such as TRICARE, or other group plans. But now that the Affordable Care Act has taken effect, many more Americans are entering the non-group insurance market. Which raises the question: Just how big was the pre-ACA non-group market?

That turns out to be a tricky question to answer. In part that’s because there’s so much more turnover among people with non-group policies than those with group coverage; also, many people may be covered by both group and non-group insurance, either simultaneously or at different times in any given year. The Kaiser Family Foundation, which has diligently tracked all manner of data related to the ACA rollout, used three different approaches to estimate how many Americans relied on non-group insurance (to the exclusion of other sources of coverage) before the law took effect.

Extrapolating from insurance-company data yielded an average monthly non-group enrollment of 10.9 million in 2011 and 2012. The Survey of Income and Program Participation found that in the fall of 2011, 11.3 million people had non-group coverage only. And based on the ASEC supplement to the Current Population Survey, Kaiser estimated that in 2011 about 11 million non-elderly Americans had insurance bought directly from an insurer as their only source of coverage.

Kaiser notes that historically, the non-group market has acted as a supplement to employer-based insurance or government coverage, and that “the number of people who have and keep non-group coverage as their primary source of protection is considerably smaller than the number of people in the market at any given point in time.” But under the ACA, that dynamic is likely to change: The Congressional Budget Office estimates that by 2016, 18 million more Americans will have non-group coverage.

Health Care
Drew DeSilver  is a senior writer at Pew Research Center.