ST. PAUL, Minn. (AP) - A long-awaited study on nurse staffing levels at Minnesota hospitals has prompted fresh division between nurses and their employers.

The Minnesota Nurses Association had hoped the state's study would help nail down firm patient-to-nurse ratios. But the research didn't find cause and effect in staffing levels and patient outcomes.

The nurses' union blamed hospitals Monday for not handing over enough data to state researchers. Minnesota Hospital Association spokeswoman Wendy Burt tells reporters many of their facilities didn't keep the detailed information researchers wanted.

Staffing levels were crucial to nurses' demands in a 2010 contract dispute that led to a one-day strike. Nurses later approached lawmakers seeking statewide staffing ratios in 2013.

Instead, the Legislature approved a study and required hospitals to post their staffing levels online.