There’s no one data source to tell us whether, when the ball drops in Times Square, more Americans will have private health insurance.

“There’s no way we’ll be sure,” says Larry Levitt, senior vice president of Kaiser Family Foundation. “There are a whole number of uncertainty and missing pieces.”

“It’s the exact opposite of weather forecasting,” says Stan Dorn, a senior expert at the Urban Institute, who has spent decades studying health coverage expansions. “There, you can be pretty confident of what will happen tomorrow but no idea about the future. Here it’s the reverse: Over time there will be significant gains, but that will take years, not months.”

Much of the challenge stems from the fact there’s no one data source that tracks who is gaining insurance coverage and who has lost, or canceled, their policy. The data that we do have can be difficult to piece together. Some states have estimated the number of Americans whose insurance policies were canceled under the Affordable Care Act, according to the National Association of Insurance Commissioners. They’ve done that by by sending out surveys to health insurers asking them what products they plan to offer in the coming year and which will be discontinued.