Online insurance exchange markets, sparked by the Affordable Care Act, open to shoppers Tuesday.

The University of Montana's Bureau of Business and Economic Research expects a bellwether day.

Bureau research found 350,000 Montanans who are already insured may change their health insurance because of Obamacare.

The Bureau said the insurance exchange will provide opportunity to 195,000 Montanans who don't have health insurance at all. That's almost 20 percent of Montana's population.

"And they don't have it for a whole variety of reasons," said the bureau's interim health care director, Paul Polzin. "Some have pre-existing conditions and can't get it. Some think health care insurance is too expensive and can't buy it. And there are some people we're calling 'the invincibles' who just think they'll never get sick."

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