Using a survey fielded by the RAND American Life Panel, we estimate a net gain of 9.3 million in the number of American adults with health insurance coverage from September 2013 to mid-March 2014.

The survey, drawn from a small but nationally representative sample, indicates that this significant uptick in insurance coverage has come not only from enrollment in the new marketplaces established under the Affordable Care Act (ACA), but also from new enrollment in employer coverage and Medicaid.

Put another way, the survey estimates that the share of uninsured American adults has dropped over the measured period from 20.5 percent to 15.8 percent. Among those gaining coverage, most enrolled through employer-sponsored coverage or Medicaid.

Although a total of 3.9 million people enrolled in marketplace plans, only 1.4 million of these individuals were previously uninsured. Our marketplace enrollment numbers are lower than those reported by the federal government at least in part because our data do not fully capture the surge in enrollment that occurred in late March 2014.

Using the RAND American Life Panel, a nationally representative panel of individuals who regularly participate in surveys, we have conducted monthly surveys since November 2013 about insurance choices and public opinion. This particular survey work—which is ongoing—is known as the RAND Health Reform Opinion Study (RHROS). We match these data with data collected in September 2013 about insurance choices. The results presented here are based on 2,425 adults between the ages of 18 and 64 who responded in both March 2014 and September 2013.

People shift from one type of health insurance to another for a number of reasons, such as job changes or marital status changes. Our survey work can't say for certain which of these shifts are due to the ACA and which are due to other factors, but we can draw some limited conclusions. A more detailed report describing the results summarized below can be found here.

Of the 40.7 million who were uninsured in 2013, 14.5 million gained coverage, but 5.2 million of the insured lost coverage, for a net gain in coverage of approximately 9.3 million. This represents a drop in the share of the population that is uninsured from 20.5 percent to 15.8 percent.

The 9.3 million person increase in insurance is driven not only by enrollment in marketplace plans, but also by gains in employer-sponsored insurance (ESI) and Medicaid.

Enrollment in ESI increased by 8.2 million.

Medicaid enrollment increased by 5.9 million. New enrollees are primarily drawn from those who were uninsured in 2013, or those who had “other” forms of insurance, including Medicare, retiree health insurance, and other government plans.

According to our estimates, 3.9 million were covered through the state and federal marketplaces as of mid-March 2014. This figure does not fully capture the enrollment surge that occurred in late March.

For most people the ACA has not changed their health insurance coverage. Among adults, 80 percent still had the same form of coverage in March 2014 as in September 2013. Notably, more than 100 million had ESI before and have ESI now, while 26 million remain uninsured.

Of those who were previously uninsured but are now insured, 7.2 million gained ESI, 3.6 million are now covered by Medicaid, 1.4 million have signed up through a marketplace, while the remainder gained coverage through other sources.

Our estimates suggest that only about one-third of new marketplace enrollees were previously uninsured. While this percentage seems low in absolute terms, it is slightly higher than an earlier figure reported by McKinsey & Company. [1]

Among the 7.8 million people who were enrolled in off-marketplace individual market plans in early 2014, 7.3 million were previously insured; 5.4 million were previously insured through an individual market plan.

Less than one million who previously had individual market insurance transitioned to being uninsured. While we cannot tell if these people lost their insurance due to cancellation or because they simply felt the cost was too high, the overall number represents less than one percent of people between the ages of 18 and 64.

The survey results reported here were collected through March 28, 2014, but many panelists responded earlier in the month and may have made new insurance choices since then. Respondents will be surveyed again in April and our figures will be updated when new data is available.

Given the strong interest in understanding the impact of the ACA, a variety of different organizations, including the Urban Institute, are conducting surveys to estimate the impact of the ACA on insurance enrollment. When making comparisons, it is important to keep in mind that there is always a margin of error. In this case, because we are extrapolating from a small survey to the entire U.S. population, the margin of error is relatively large. For example, while we estimate 9.3 million individuals become newly insured, the margin of error is 3.5 million people.[2] Furthermore, the timing of surveys may vary. Given the surge in enrollment at the end of March, whether that period is included in the survey may dramatically affect results. Thus, it should not be surprising that our estimates may not match perfectly.

Over the coming months and years, further change can be expected as people become more familiar with the law, the individual mandate penalties increase to their highest levels, the employer mandate kicks in, and other changes occur. But early evidence from our survey indicates that the ACA has already led to a substantial increase in insurance coverage. Consistent with the design of the ACA, this gain in insurance has come not only from new enrollment in the marketplaces, but also from new enrollment in employer coverage and Medicaid.

Katherine Grace Carman is an economist and Christine Eibner is a senior economist at the nonprofit, nonpartisan RAND Corporation.

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