This article was updated on Oct. 21 to reflect new information about the ballot question. See our full coverage of the 2018 Massachusetts ballot questions. Download WGBH News' one-page voter guide on Ballot Question 1.

Should there be a legal cap on the number of patients assigned to one nurse? That’s the crux of Massachusetts' Ballot Question 1, which voters will decide on Nov. 6.

The issue has been debated for many years, but this year, the issue threatens to divide the medical community. Some say if this ballot initiative passes it could fundamentally change the state's health care system.

Here’s a look at the issue, the data and the potential impact. Read the ballot measure here.

1. What would the ballot measure do?

If voted into law, this measure would limit how many patients one nurse could care for in hospitals across Massachusetts.

The mandated limits would vary based on the unit and level of care required. For example, a nurse could have no more than one patient if that patient is under anesthesia. A nurse could have no more than four pediatric patients at any given time. In the psychiatric department, a nurse would be responsible for five patients at most.

If hospitals violate these ratios, they could be fined up to $25,000 per incident.

The law would also prohibit hospitals from reducing other hospital staff — like clerical or maintenance staff — in order to comply with nurse staffing ratios.

If there’s a public health emergency, declared by the state or federal government, then these ratios could be temporarily suspended. But when it’s not an official emergency but things are busy — for example, if there was a bad accident on the interstate — these ratios would have to be followed.

The mandated staffing levels would go into effect Jan. 1, 2019 or, if there’s a collective bargaining agreement in place, the mandate would kick in as soon as the contract is up.

2. Who supports the ballot initiative?

The Massachusetts Nurses Association, a union that represents about 20 percent of nurses in the state, is the main force behind this ballot initiative.

They say mandating staffing levels is key to patient safety.

They point to dozens of studies that show better patient outcomes when nurses are assigned fewer patients. They argue the current situation has led hospital executives, driven by the bottom line, to make unsafe staffing decisions. The result, they argue, is medical errors, more hospital-acquired infections, longer patient stays, more re-admissions and high nurse burnout. In short, they say, the status quo is dangerous for patients.

A study commissioned by the Massachusetts Nursing Association found 90 percent of nurses surveyed — a little less than half of whom were members of the association — said they did not have enough time to "properly comfort and assist patients and families." Further, 77 percent reported medical errors, including wrong medications and dosage. (Read summary here.)

Sandy Keenan works at Tufts Medical Center and has been a nurse for 28 years. She supports the initiative and says hospital administrators don’t listen when nurses say they are overburdened.

“It’s just like childcare," she explained. "Would you send your child to a daycare where one person has an unlimited number of children?”

3. Who opposes these changes?

The Massachusetts Health and Hospital Association opposes the ballot initiative. Some nurses groups are teaming up with them, including the Massachusetts chapter of the American Nurses Association and the Organization of Nurse Leaders.

They say the proposal is dangerous and would undermine the quality of patient care.

Staffing is a delicate science, they argue, and this measure is a blunt tool. It takes decision-making authority out of the hands of doctors, nurses and hospital administrators, limiting their ability to use their expertise and best judgment in a crisis.

They believe patients will notice a couple problematic changes. Here are two big ones:

First, they say, there will be much longer wait times.

They worry about a scenario that goes something like this: You’re in the emergency room and need to head to the intensive care unit, but every nurse up there is already serving the maximum number of patients allowed. So you are stuck waiting in the ER, and the ER then can’t take in any other patients because that would put an ER nurse over their limit. The system gets gummed up, and patients end up waiting much longer.

“The Emergency Department is going to back up and patients won’t have access to emergency services. That’s the reality,” said Deborah Cronin-Waelde, the chief nursing officer at Melrose Wakefield Healthcare.

Second, programs — maybe even whole hospitals — will close.

The measure could take such a financial toll that hospitals will be forced to cut back on services, said Doug Brown, the president of two community hospitals affiliated with UMASS Memorial Health Care. He said all hospitals would be hit hard, but especially the small ones.

“Unfortunately, when we have to close programs, it is often the programs that provide care to the most vulnerable that are the first on the chopping block,” Brown said. “That’s only because those are programs that lose money.”

He also says some of the increase cost could be passed on to people through higher insurance premiums.

4. What would this cost?

The pro and con campaigns have offered wildly different cost estimates.

Those advocating for the ballot measure suggest this law would cost about $47 million a year to implement. That’s a fraction of what the opponents estimate. They suggest the law could cost $1.3 billion the first year and $900 million a year after that.

Just five weeks before election day, the Health Policy Commission — an independent state agency — weighed in. In a report, they said the measure would cost between $676 million and $949 million annually after the first year. And, they warned, this is likely a conservative estimate because of the limited staffing data available to them.

The HPC said such costs could lead to the closure of unprofitable units and higher insurance premiums, among other things. The increases come from the cost of hiring a couple thousand more nurses, the predicted wage increases for nurses, and the cost of implementing the law at state-operated hospitals.

The HPC analysis largely backed up the claims made by those opposing the measure. Advocates blasted the HPC, questioning why it did the analysis in the first place and whether the group is biased. Advocates contend the analysis was conducted too quickly and did not use independent data sources to determine the cost estimates.

This is the first time the HPC has analyzed a ballot question. They defended the choice, saying it is part of their responsibility to examine anything that might contribute to an increase in healthcare spending.

As part of the ballot measure, the Health Policy Commission would implement the law and monitor compliance.

5. Are there enough nurses?

Those opposed to the measure say there are not enough nurses to meet the stipulated staffing levels. They say there’s already a nurse shortage and that the ballot initiative would require hiring thousands of new nurses in short order.

They say the scramble to hire enough nurses could mean hospitals pull them from places like nursing homes, and those new hospital nurses may be less experienced.

Advocates of Ballot Question One point out that Massachusetts has among the highest number of nurses per capita. Plus, they say with better working conditions, there will be less nurse burnout and some nurses who left the profession may return.

6. Are there already mandated staffing limits?

Yes, but only in intensive care units in Massachusetts hospitals.

Since 2014, nurses in ICUs can be assigned a maximum of two patients at any given time. This was the result of a compromise. It happened in response to two ballot initiatives that would have created a lower cap on the nurse-to-patient ratio in ICUs and placed certain regulations on hospital finances. The initiatives were withdrawn when the ICU staffing level was agreed upon.

7. Do any other states do this?

One other state: California.

Similar legislation on nurse staffing passed in California in 1999, and it was implemented in 2004. Joanne Spetz, a professor at the University of California, San Francisco, has been studying the results ever since.

“Overall, there is evidence of what I would describe as better nurse outcomes — more satisfaction, better pay, less burnout, lower injury rates,” she said.

When looking a number of measures of patient outcomes, not much changed. “Maybe hiring more RNs, but laying off your aides, meant that you had an improvement in one area and then you had something get worse in another area,” says Spetz. “When you look at patient outcomes, it’s a wash.”

And the threatened program closures and emergency room wait times?

Spetz says that those things did not materialize in California. Anecdotally, she says there may have been problems in the first few weeks, but hospitals moved people around and things worked out okay.

However, there are a few key differences between the Massachusetts ballot measure and the California legislation.

First, the Massachusetts ballot measure requires hospitals to meet the nurse-patient ratios without changing other hospital staffing levels. In California, that was one key way hospitals made the finances work, but it may explain why patient outcomes did not seem to improve.

Second, if Massachusetts voters approve this initiative, it goes into effect much more quickly than the California law, which gave hospitals years to scale up.

Third, Massachusetts ratios would be set for the foreseeable future. In California, there is a way to adjust the ratios as technology and other things change.

Spetz won’t say what she’d recommend. Instead, she said, “It’s not a clear-cut policy decision and, if it were, you wouldn’t have a ballot proposition. It would have been done already.”

Read WGBH News' one-page voter guide on Ballot Question 1: