A much-anticipated state study on the number of nurses required to provide safe, effective patient care in Minnesota hospitals fell short of its goals after hospitals failed to provide the data to answer key staffing questions.

The lack of hospital participation drew fire Monday from the state’s nurses union, which hoped the study would fortify its negotiating position on the need for lower patient-to-nurse staffing ratios. “Are they just unwilling to cooperate with a study they themselves agreed to with our lawmakers?” said Linda Hamilton, president of the Minnesota Nurses Association.

A spokeswoman for the Minnesota Hospital Association said its members cooperated with the study, but simply lacked the detailed data that researchers sought.

In lieu of a fresh analysis of nurse staffing in hospitals, state health economics researchers summarized existing research, and found that higher nurse staffing has been associated with lower rates of falls, deaths and surgical complications.

However, existing research doesn’t prove cause and effect, nor does it suggest that an immediate infusion of nurses in Minnesota’s hospitals would improve patient safety, Dr. Edward Ehlinger, state health commissioner, said in a Jan. 16 letter to lawmakers.

The results “do not identify points at which staffing levels become unsafe or begin to have negative effects on outcomes,” Ehlinger wrote.

Nurse staffing was a central issue in contentious negotiations between nurses and 14 metro-area hospitals that led to a one-day strike in 2010. Nurses conducted walkouts and pickets on June 10 that year, demanding that hospitals stick to predetermined nurse ratios to ensure patient safety, forcing the hospitals to hire temporary replacements to get through the day.

However, nurses relinquished the demand for mandatory ratios a month later, after the hospitals sweetened their three-year contract offers with better pay and pension and health benefits.

In 2013, the union switched from the sidewalks to the Legislature, seeking a state law that would mandate hospital nurse-to-patient ratios. Instead, lawmakers approved the staffing study and required hospitals to publicly report their nurse staffing levels online.

“Nurses fought for this study at the Capitol in 2013 because they knew that a rigorous, objective study of nurse staffing would show patients do better when enough nurses are on duty,” Hamilton said.

A work group that included hospital and nursing leaders decided that the study would need more data than was publicly available to determine whether nurse-to-patient ratios improve care. So they asked 39 participating hospitals to provide daily, unit-specific counts of patients and nurses in 2013.

Only one was able to respond with data — Hennepin County Medical Center — because the rest didn’t have the capability to go back and collect staffing and patient counts at such a detailed level, said Wendy Burt, a spokeswoman for the state hospital association. Burt stressed it was a logistical issue rather than an unwillingness by hospitals to support the study, which reaffirmed that nurse staffing is important but that ratios are unproven and difficult to calculate.

“Caring for a patient is done by a whole care team, including physicians, including nurses,” Burt said, “but also including other members as needed by the patients’ illnesses or conditions — from nursing assistants to respiratory therapists to dietitians.”

The next round of contract talks between Twin Cities nurses and hospitals is slated to begin next year, but how the report will shape negotiations is unclear.

While the 2013 nurse staffing legislation didn’t require ratios, it did require public reporting on the Minnesota Hospital Quality website of staffing levels in individual hospital units such as maternity and intensive care.

Burt said hospitals leaders are no doubt using this as a benchmark to make sure their nurse staffing levels, measured in nurse hours worked per day, are in line with competitors.