People who were eligible for coverage at HealthCare.gov and who visited the site in December tended to report good health, according to new figures that point to the possible makeup of ObamaCare's emerging risk pools.
Only limited conclusions may be drawn from the data, which pertains to eligible users at HealthCare.gov and not necessarily people who applied for coverage under ObamaCare.
But researchers said the study contained good signs for enrollment under the law, a crucial factor for future prices on the exchanges and healthcare reform's wider success.
The "large share of visits by young adults and people in good health" is "encouraging," said lead researcher and Commonwealth Vice President Sara Collins in a statement.
"Their participation will be critical to the marketplaces' success over time," Collins said.
The Commonwealth Fund is a New York-based research foundation that supports the healthcare law.
According to its study, 77 percent of eligible visitors to HealthCare.gov by the end of December reported being in good, very good or excellent health.
The plurality (41 percent) tended to be younger adults, ages 19 to 34, who are generally the cheapest to insure. About one-third were ages 35 to 49, and 28 percent were 50-to-64-year-olds, who tend to be the most expensive group.
The age distribution mirrors the population that is potentially eligible for coverage under ObamaCare, researchers wrote, suggesting that HealthCare.gov is attracting a representative sample of the group it was designed to reach.
That is good news for the Obama administration, but it comes with a catch: fewer than two in five visitors to the marketplaces actually applied for coverage by Dec. 31.
That rate is not a big surprise. From the site's launch on Oct. 1, sign-ups at HealthCare.gov have not kept pace with the system's sustained and heavy traffic.
Administration officials note that consumers can take weeks or months to shop for health insurance and express hopes that eligible visitors to HealthCare.gov will ultimately pick plans by the end of March.
Thursday's survey provided evidence that at least some site visitors will return and complete the process, though many eligible patients still have not sought to access the system.
Only one-quarter of potentially eligible consumers had visited a marketplace by Dec. 31. Still, 59 percent said they would enroll by the end of the sign-up period.
The report comes at a crucial time for the Obama administration.
While the immediate political firestorm over healthcare has abated, officials still face a heavy lift in achieving the 7 million enrollments projected by March 31. About 2.1 million people signed up for private plans on the federal and state marketplaces by the end of December, the administration recently said.
The White House is also under pressure to release information about the age distribution of people signing up for exchange coverage.
The Department of Health and Human Services has not said that it will never publish the details, but has failed to do so thus far despite repeated calls from the press.
Commonwealth's research found that a majority (69 percent) of visitors continue to describe their experiences at HealthCare.gov as fair or poor, despite marked improvements in the site's functioning.
The survey was conducted by phone from Dec. 11-29 of 622 potentially eligible adults and has a margin of error of about 4.6 percent.