New Yorkers who've bought health insurance through the state's Affordable Care Act marketplace are paying premiums that cost about half as much, on average, as the coverage would have last year. And one in three enrollees is relatively young. That all bodes well for the state's push toward universal coverage.

The online exchange, called the New York State of Health, provides a convenient way for people without job-based insurance to shop for a plan. As of last week, 949,428 people had enrolled via the exchange. Many qualified for Medicaid or Child Health Plus, but 429,894 signed up for insurance from private companies -- 34 percent of them younger than 35. For Long Island residents, monthly premiums for a standard HMO have dropped to as low as $482 from $1,534 for a similar plan in 2013, according to the state health department.

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For this first year of the law, insurers set premiums for policies on the exchange based on their best guesses about what providing the coverage would actually cost. But when premiums are set for 2015, insurers will base them on a year's experience of actual costs. That's when we'll see whether this year's significant savings are sustainable.

The increase in the number of people buying their own private insurance this year -- way up from 17,000 in 2013 -- is the primary reason for the dramatic reduction in premiums, state officials said. And even before the Affordable Care Act became law, New York required insurers selling plans directly to individuals to cover policyholders' adult children and participants with pre-existing conditions. The plans also had to be priced without regard to factors like age and gender. Those costs were already baked into the cost of coverage here, so when the law's individual mandate drove up the number of people buying insurance -- many of them young and healthy -- costs tumbled. So far so good.