The Covered California exchange, on the other hand, has enrolled more than 1 million people in private insurance plans after being allocated $1.06 billion in federal funds—for an average dollar allocation of $1,046 per enrollee. That makes California the most efficient state-run exchange, according to CNBC.com's analysis that divided the total federal dollars allocated by private plan enrollees.
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While that yawning gap between the two states is striking, there are also wide differences between the 13 other states running their own Obamacare exchanges.
Exchanges in New York and Washington state, for example, each have an average dollar allocation per enrollee of less than $1,400.
But two of their respective neighbors—Massachusetts and Oregon—have averages of $6,832 and $6,044, respectively.
And the Washington, D.C., exchange, which ranked as the second least efficient, has a whopping average of $20,449 per enrollee. That's $13,588 more than the third least efficient state by that metric, Vermont.
Sanjay Singh, CEO of hCentive, a health insurance tech company that was involved in building exchanges for New York, Colorado and Kentucky, said that the question of why some states "are doing worse than others is almost independent of the dollar amounts they took."
Instead, Singh said, it is more a function of variables including their management structure and the vendors they used to build the exchange.
But with the close of Obamacare's open enrollment on Monday, these variations and large dollar amounts are raising questions of whether many states that opted to run their own exchanges would have seen better results—and spent less taxpayer money—if they had let the federally run HealthCare.gov exchange handle that job. HealthCare.gov is doing just that for 36 other states.
In all, about $3.87 billion in federal money was allocated to the 15 exchanges run by the states and the District of Columbia, for an average of $1,899 per private plan enrollee so far.
While the average does not take into account enrollments for people newly eligible for government-run Medicaid programs by those exchanges, the analysis gives a snapshot of the exchanges' relative successes to date.
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"Just obscene amounts of money have disappeared into these state exchanges for very little actual performance," said Phil Kerpen, president of the free market advocacy nonprofit group American Commitment. "You just have this huge duplication and waste in places like Hawaii and Oregon."
"How does a state like Vermont spend as much money as it did?" Kerpen said. That small state has been allocated $168 million in federal funds, with an average per enrollee of $6,911.