© Andrew Harrer/Bloomberg
The fight over how to define the new health law's success is coming down to one question: Who counts as an Obamacare enrollee?

Health insurance plans only count subscribers as enrolled in a health plan once they've submited a payment. That is when the carrier sends out a member card and begins paying doctor bills.

When the Obama administration releases health law enrollment figures later this week, though, it will use a more expansive definition. It will count people who have purchased a plan as well as those who have a plan sitting in their online shopping cart but have not yet paid.

"In the data that will be released this week, 'enrollment' will measure people who have filled out an application and selected a qualified health plan in the marketplace," said an administration official, who requested anonymity to frankly describe the methodology.

The disparity in the numbers is likely to further inflame the political fight over the Affordable Care Act. Each side could choose a number to make the case that the health law is making progress or failing miserably.

On Monday, the Wall Street Journal, citing anonymous sources, said insurance companies have received about 50,000 private health plan enrollments through HealthCare.gov. Even combined with state tallies, the figure falls far short of the 500,000 sign-ups the administration initially predicted for both private sign-ups and those opting for the expansion of Medicaid.

In recent weeks, administration officials have warned that the enrollment figures for October would be low, given the tumultuous launch of the health Web site.

The administration plans to use this count of enrollees because that's where their interaction with the healthcare.gov site ends, the administration official said. Insurance plans, rather than the federal government, are responsible for collecting the first month's premium.

The shopping cart on healthcare.gov only contains space for one health plan, meaning the consumer must have gotten far enough to settle on a specific option.

Addressing the Wall Street Journal's report, Health and Human Services spokeswoman Joanne Peters said: "We cannot confirm these numbers. More generally, we have always anticipated that initial enrollment numbers would be low and increase over time. .โ€‰.โ€‰. The problems with the Web site will cause the numbers to be lower than initially anticipated."

States that have so far released enrollment data also tend to use this wider definition. The 14 states running their own insurance marketplaces have reported 49,000 enrollments in private health insurance plans, according to an analysis released Monday by consulting firm Avalere Health. They have also enrolled many thousands more into the Medicaid program, which the health-care law expanded.

"The idea that people are going to do layaway purchasing three months out goes against the American way," Rhode Island exchange director Christine Ferguson said in late September, shortly before the health law's rollout.

Different definitions of enrollment lead to vastly different estimations of who will gain coverage under the Affordable Care Act. In the District of Columbia, for example, health insurance plans reported signing up five people during the health law's first month.

But the city's exchange, DC Health Link, estimates that 321 people in the District have dropped a specific health insurance plan into their shopping cart. Of those, 164 have requested an invoice for their first month's premium from the insurance carrier.

"We recognize that most people do not have the luxury of paying for coverage in October, months before a bill is due," exchange spokesman Richard Sorian said Friday. "I hope that all consumers here in the District remember that they have until Dec. 15 to finalize their selection by paying their first month's premium in order to have coverage on Jan. 1, 2014."

Sarah Kliff covers health policy for the Washington Post. Sarah joined the Post in August 2011 from Politico, where she authored Politico Pulse, a daily health policy tipsheet. Prior to Politico, Sarah was a staff writer at Newsweek covering national politics. Her writing has appeared in National Geographic, the BBC, Humanities Magazine and St. Louis Magazine. She is the recipient of fellowships from the Kaiser Family Foundation and University of Southern California Annenberg School of Journalism.