Higher Nurse-to-Patient Ratio Law Improves Nurse Injury Rates by One-Third

May 6th, 2015 10:06 am ET - Paul Leigh, Ph.D.

CDC - NIOSH Science Blog – Higher Nurse-to-Patient Ratio Law Improves Nurse Injury Rates by One-Third

California is the only state with a law governing minimum nurse-to-patient staffing ratios. The ratios vary depending on the type of hospital service but are in the range of one nurse for every five patients. (The ratios are available on the California Department of Public Health website

.) The law went into effect in 2004.

Lawmakers and stakeholders intended that the law would improve patient safety as more nurses were employed to care for the same number of patients. Whereas many studies show improved patient safety after 2004, no consensus in the scientific literature has emerged.

My colleagues and I sought to answer a different question: could the law improve safety for the nurses themselves? We found that indeed the law did improve safety for nurses and the results were published in the May 2015 issue of the International Archives of Occupational and Environmental Health

, “California’s Nurse-to-Patient Ratio Law and Occupational Injury”.

We began with the U.S. Bureau of Labor Statistics’ data set entitled the Survey of Occupational Injuries and Illnesses (SOII). The SOII collects annual data on nonfatal injuries and illnesses derived from 150,000 to over 200,000 private firms, depending on the year. We selected injury and illness data from 1999 to 2009 and combined with data on employment in hospitals in California and the rest of the US from the SOII and the California Employment Development Department. We applied the “difference-in-differences” method whereby the change in injury and illness rates before and after implementation of the law within California were compared to changes in injury rates for the same time period in the 49 other states and DC combined .The “difference-in-differences” method attempts to mimic a randomized trial, based on the assumption that a policy change is enacted independent of the underlying temporal trend in that population’s outcomes. This method helped us account for a nationwide downward trend in workplace injuries and separate the effects of California’s staffing mandates attributable to the new law. We compared differences in years for 2001 to 2003 with 2005 to 2007 for both California and the other 49 states combined.

We found that the law was associated with 55.57 fewer occupational injuries and illnesses per 10,000 registered nurses (RNs) per year, a value 32% lower than the expected rate without the law based on injury and illness rates before the law was enacted. The corresponding estimated reduction in injury and illness rates for licensed practical nurses (LPNs) was 38%.

While the data don’t tell us why the rates went down, the improved staffing ratios could lower rates of injuries and illnesses to nurses in a number of ways. For example, back and shoulder injuries could be prevented, if more nurses were available to help with repositioning patients in bed. Likewise, fewer needle-stick injuries may occur if nurses conducted blood draws and other procedures in a less time-pressured manner. Further research is needed to see if these reductions are maintained over time.

Are you aware of efforts in other states to try to reduce nurse to patient ratios? Please let us know in the comment section belwo.

Paul Leigh, Ph.D.

Dr. Leigh is a professor in the Department of Public Health Sciences and the Center for Healthcare Policy and Research at the University of California Davis School of Medicine.

Other study authors, also from UC Davis, were Patrick Romano of the Center for Healthcare Policy and Research and the Department of Internal Medicine, Ana-Maria Iosif of the Department of Public Health Sciences, and Carrie Markis of the Betty Irene Moore School of Nursing.

The research was funded, in part, by the National Institute for Occupational Safety and Health (U54OH007550-11) and the California Department of Public Health (Agreement 09-11543).