ST. PAUL — The number of people who signed up for insurance through Minnesota’s online exchange nearly tripled from its first two weeks of operation to its second two weeks, but it’s impossible to say whether MNsure is succeeding in the key goal of the federal health overhaul: reducing the number of people without insurance coverage.

MNsure officials said Wednesday that about 10,940 people signed up for insurance in the site’s first month of operation and an additional 4,328 people completed the application process but haven’t yet picked an insurer. What’s lacking is an accounting of how many of those enrollees previously did not have insurance.

The reason? MNsure isn’t asking.

“Our application itself does not ask what someone’s previous coverage was,” said April Todd-Malmlov, MNsure’s executive director. “It’s not a required question to ask if someone previously had coverage.”

Todd-Malmlov acknowledged that reducing rates of the uninsured was among the chief goals of the health care law championed by President Barack Obama and passed by Congress in 2009. While Minnesota is one of 14 states operating its own exchange rather than deferring to federal control, Todd-Malmlov said MNsure’s application was based on a standard federal application that also doesn’t ask whether enrollees previously had insurance.