In a concept in behavorial science, policymakers identify incentives for people to make decisions that are better for them and for society. The key to the approach, called "nudging," is motivating people to make a particular choice without making them feel a decision was forced on them.

Nestled within a centrist Republican proposal to replace Obamacare is a concept called auto-enrollment that aims to use the nudging principle, and proponents believe it would reduce the number of uninsured while gutting the unpopular individual mandate requiring people to obtain insurance or pay a penalty.

Auto-enrollment was part of the conversation when Obamacare's individual mandate was challenged in the Supreme Court and has appeared in various Republican proposals since the law's passage, including one bill House Speaker Paul Ryan, R-Wis., introduced in 2009. Now, it is being raised again by centrist Republicans in legislation authored by Sens. Bill Cassidy of Louisiana and Susan Collins of Maine.

Through their bill, the Patient Freedom Act, states would decide not only whether they want to keep Obamacare but also whether they want to craft their own proposals, which could include an auto-enrollment provision. Residents would be provided with a federally funded, age-adjusted tax credit that would go into a health savings account so that they could buy a private insurance plan. Households that don't use the credit would be enrolled automatically in a basic, or catastrophic, plan with the amount of the credit going to insurers to pay for premiums.

"It wouldn't preclude people from taking more generous coverage, but it can discourage them from opting out because they would be throwing away the tax credit," said Mark Pauly, professor of healthcare management at the Wharton School of Business at the University of Pennsylvania. "It's a fairly clever idea to make people do what they ought to without feeling too persecuted with it."

The plans would come with high deductibles but shield patients from paying more than a certain amount if they faced a medical emergency. Patients would have the option to buy better coverage during open enrollment or to opt out entirely.

"It's sort of a minimal intervention which in principle allows autonomy, but also takes advantage of inertia," said Scott Harrington, healthcare management professor at Wharton. "The idea is that you might be able to nudge people into a decision that is better than the alternative of doing nothing, but it still allows them the freedom to do something else."

The approach hasn't been at the forefront of debate on Capitol Hill, but some lawmakers and President Trump have begun to openly question whether a centrist approach to healthcare may be the best way to arrive at an agreement.

Lawmakers are increasingly recognizing that some impetus is needed to keep the popular provisions created under Obamacare, such as banning insurers from discriminating against people with pre-existing conditions. Republicans' solution in the American Health Care Act was to require people who let their coverage lapse to pay 30 percent more for coverage when they did sign up.

Even now, as Obamacare has struggled to gain traction among young and healthy enrollees, policymakers have questioned if the individual mandate penalty should have been higher or if another approach would work better.

Asked about auto-enrollment, Andy Slavitt, the administrator for the Centers for Medicare and Medicaid under former President Barack Obama, tweeted it was "in the category of workable ideas."

Research in the area of what people do when faced with defaults has been increasing. Studies show, for instance, that workers who are enrolled automatically in pensions tend to stick with them.

"If the decision process is flipped where people are put into something and given the option to get out, the vast majority of people stick with it and they are happy with it," said James Capretta, a fellow at the conservative American Enterprise Institute, which wrote a version of the proposal. "Almost certainly the same would play out with health insurance."

The concept of encouraging people to make particular decisions gained popularity in the 2008 book Nudge by economists Richard Thaler and Cass Sunstein. To qualify as a "nudge," a policy must not be required and must be easy and inexpensive to avoid.

"The idea is to try to arrive at a policy that is non-coercive by taking advantage of the fact that people will stick with what they have unless there's a damn good reason not to," said David Anderson, research associate in the Health Policy Evidence Hub at Duke University's Margolis Center for Health Policy.

But when it comes to health insurance, a "nudge" may be hard to define. Among voters whose greatest concern is about liberty and personal responsibility, the auto-enrollment proposal is troubling, particularly because it would allow the government to choose plans for people.

"There are some people who don't like it because it feels like the government making decisions on behalf of people," Capretta said.

To conservative-leaning voters, the policy may be understood as worse than Obamacare.

"The key for a healthy private individual market is getting young and healthy people to enroll in coverage when there is a good chance they'll be paying a good bit for coverage they won't end up needing," said Nicholas Bagley, a regulatory law expert at the University of Michigan Law School. "The individual mandate is one way to get them in, and auto-enrollment is another way. Which one is most appealing depends on the degree to which you think the government action is coercive."

The policy also would face numerous logistical hurdles, including the extensive task of identifying the 29 million people who are still uninsured.

"The data is not always easy to compile, certainly not in real time," Bagley said.

Capretta offered a few solutions, including enacting auto-enrollment when people go to the hospital, doctor's office or DMV, or using information from the IRS that has been collected for Obamacare. He acknowledged the process would take a few years to become more refined.

But even then, it's not clear the approach would rein in costs for individuals or the federal government. States would need to debate what a catastrophic plan would look like, what constitutes a medical emergency and how much each tax credit would be.

Even if a medical emergency were covered, lawmakers would need to make decisions about coverage for ongoing care that came as result of an accident, for instance, such as physical therapy, imaging or other testing. States and even regions and individual hospitals vary significantly in how much they charge for services. Out-of-pocket costs could be significant for patients.

"That's a big question mark," Anderson said about the cost. "It really depends how much money you want to spend for the premium."

The amount and level of care could play into public perceptions about how coercive the policy becomes and whether it becomes too burdensome for people to default to the plan state governments select.

"It makes sense when it is something that is more or less good for people, unequivocally," Pauly says of the auto-enrollment option. "The main reason someone wouldn't do it is if it enrolled them into an option that wasn't good for them."