Whatever its flaws, the Patient Protection and Affordable Care Act has sparked innovation across the U.S.’s sclerotic health-care system. An especially welcome example is the push to expand the role of nurse practitioners in primary care.

The country’s 171,000 NPs are trained to do many jobs that primary-care doctors do: diagnose problems and treat patients, order tests, prescribe drugs and refer to specialists. And with an average income of $99,000, they’re a bargain; the average family medicine physician makes twice that after six years’ practice.

What NPs have not been able to do in most states is practice those skills without a doctor looking over their shoulder. Seventeen states allow it; 12 do not; and the rest fall somewhere between, requiring some degree of physician supervision.

President Barack Obama’s health-care law, which will extend insurance to an estimated 25 million more Americans, may get states to lift those restrictions. California is already considering it, as are Pennsylvania, Michigan and Massachusetts, according to the Wall Street Journal. Health-care groups and even the National Governors Association have urged states to loosen the rules.

This would be a good idea even if the patient population weren’t about to balloon. There’s no evidence that limits on nurse practitioners’ roles protect patient safety. A 2002 literature review in the British Medical Journal found that people were more satisfied with the care they received from NPs than they were with doctors’ care, and such care didn’t lead to any differences in health outcomes, return consultations, prescriptions or referrals. Subsequent papers have reached the same conclusions.

Even the American Medical Association, which opposes allowing NPs to practice independently, concedes that there is no evidence that patients get inferior care from them.

The more likely explanation for the continuing restrictions is resistance from doctors’ groups. The AMA spent $16.5 million on lobbying in 2012, putting it 11th out of more than 4,000 groups tracked by the Center for Responsive Politics. State medical associations spent more than $1 million on lobbying last year in both California and Texas, which are among the states that don’t allow NPs to practice without doctor supervision.

Resistance to nurses providing more care also reflects a cultural preference, an insistence that the people who diagnose us have as many years’ training as possible — even if the evidence suggests that such training may not be necessary for primary care.

The Affordable Care Act has made it increasingly difficult for states to defend that preference. The law will put even more pressure on the country’s 300,000 practicing primary-care doctors to meet demand from people who gain health insurance.

Giving NPs more autonomy won’t solve the access problem by itself, as doctors rightly point out. These providers won’t necessarily be any more motivated than doctors are to work in underserved areas. And they may continue to choose to work with doctors, even if they don’t have to.

Those aren’t reasons to keep the current rules, however. They’re just a reminder that the U.S. health-care system needs many adjustments. At least this particular fix is an easy one. State policy makers should follow the data, relax the restrictions on nurse practitioners, and move on to harder issues.

Editorial by Bloomberg View