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n this photo taken Monday March 31, 2014, applicants fill the lobby of the Oakland Asian Cultural Center waiting to enter a health care enrollment event in Oakland, Calif. The initial enrollment period for getting subsidized health coverage may have passed, but California's health insurance exchange is offering a two-week extension to accommodate the crush of last-minute applicants. A Covered California spokesman said Tuesday that consumers who were unable to create an account or start their application because of technical problems have until midnight on April 15 to finish their applications. (AP Photo/Eric Risberg)

For all the arguments, pro and con, about the effectiveness of the Affordable Care Act, there is one measurement above all upon which its first year of implementation ought to be judged:

Did it substantially reduce the number of uninsured?

There is still much processing of applications remaining to be done, and after that surveys to be taken and analyses to be conducted. But in California it is already apparent that significant progress has been made in accomplishing the program's major goal.

Just by using back-of-the-envelope math, it appears that at least a quarter and perhaps as many as half of the state's roughly 4.6 million people who didn't have health insurance last year and were eligible for coverage under the ACA have insurance today.

"Fewer people are uninsured," said Peter Lee, executive director of Covered California, speaking with reporters on the hectic final day of enrollment. "It's a big number."

About 1 million of the state's 5.6 million uninsured were ineligible for coverage under the Affordable Care Act because they are undocumented. The question is how did the remaining 4.6 million fare?

Here's some rough math, based on current enrollment figures: About 1.2 million people purchased policies through Covered California, the state's health insurance-purchasing exchange. Of them, about 1 million received federal subsidies to cover a portion of their premiums. Lee and others estimate that a majority of those who received subsidies did not previously have insurance because they could not afford it. That would mean about 600,000 newly insured.

The expansion of Medi-Cal resulted in 1.5 million enrollees, with many more applications still being processed. Although some of those people were previously covered and just happened to renew during the ACA enrollment window, it is likely that the overwhelming majority of those enrollees were not previously insured.

On top of that, there are unknown numbers of others who obtained insurance as a result of the law, including those who purchased policies through the individual market either because a pre-existing condition had previously locked them out or because they were motivated to do so by the threat of a tax penalty. In addition, a significant percentage of the estimated 430,000 California young adults up to age 26 now covered by their parents' policies were previously uninsured.

There are other unknown factors. For instance, close to 1 million Californians with individual policies were notified last fall that their policies had been canceled, a not uncommon practice even in the days before the ACA. In most cases, insurers shifted those customers to another product. Others shopped at Covered California, where they were able to take advantage of subsidies.

In addition, some number of Californians lost employer-based coverage, continuing a long-term trend of businesses dropping work-based coverage in the face of rising premiums. At the same time, some small businesses, taking advantage of new tax credits, added employee coverage. A simulation created by researchers at UCLA and UC Berkeley estimates that the net effect on employer-based coverage will be a wash.

The UCLA Center for Health Policy Research's statewide health interview survey has long been the gold standard for measuring how many Californians have insurance and through what means they obtain it. Those interviews take months to conduct, and researchers say results of the 2014 survey will not be available until the summer of 2015.

Because of the extreme interest, the center is considering a one-time, six-month estimate that would be available this fall that would show how ACA enrollment affected statewide insurance numbers.

For now, the raw numbers suggest significant progress.

"We can't pinpoint the number, but we have a ballpark figure," said Anthony Wright, executive director of the advocacy group Health Access. "There's been a substantial reduction in the number of uninsured."

The most recent simulation produced jointly by the UCLA Center and UC Berkeley Center for Labor Research and Education estimates the number of uninsured who were eligible for coverage will drop by from 1 million to 1.9 million. The numbers through the official close of enrollment, which was partly extended to April 15 in the face of overwhelming last-minute demand, suggest the higher estimate may be closer to the mark.

Lee called the close of Year One of the Affordable Care Act, "the opening of a new era in America in which health care is a right and not a privilege."

That proclamation seems a bit grandiose. At the same time, it seems undeniable that the arrival of such an era is nearer now than ever before.