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HMO penetration in a hospital's market affects the relationship between RN staffing and quality of care

Increasing registered nurse (RN) staffing seems to improve quality of care at hospitals that are at lower levels of RN staffing when the hospitals are located in markets with high HMO penetration (greater than 27.9 percent), according to a recent study supported by the Agency for Healthcare Research and Quality (HS10153). Increases in RN staffing at these hospitals were associated with fewer actual than expected in-hospital deaths (lower mortality ratio) and shorter actual than expected length of stay (lower LOS ratio). However, this was not the case for hospitals in low HMO penetration markets (less than 7.5 percent).

These findings suggest that nurse staffing decisions should be responsive to local conditions, notes Barbara A. Mark, R.N., Ph.D., F.A.A.N., of the University of North Carolina School of Nursing. Dr. Mark and her colleagues analyzed 1990-1995 data on 422 acute care hospitals in 11 states from the Healthcare Cost and Utilization Project Nationwide Inpatient Sample and other data sources on nurse staffing. They examined whether managed care penetration in a hospital's market had an effect on the relationship between nurse staffing and quality at these hospitals.

After controlling for hospital-fixed effects, increasing nurse staffing significantly reduced the mortality ratio at hospitals with lower levels of RN staffing (the 25th percentile of nurse staffing) in high HMO penetration markets. However, the benefit diminished for hospitals with more nurses, with a non-significant but still negative effect at the 50th percentile and no effect at the 75th percentile of nurse staffing. Increases in RN staffing significantly reduced the LOS ratio at both the 25th and 50th percentiles of nurse staffing, with the effect at the 75th percentile still negative but not significant. In contrast, none of the estimation methods showed a significant effect of nurse staffing on mortality or LOS ratios for hospitals in low HMO penetration markets.

An earlier AHRQ-supported study by Dr. Mark and colleagues (See the May 2004 issue of Research Activities, page 30) suggested that hospitals in high HMO penetration markets may have adopted cost control mechanisms such as case management and discharge planning. These changes may have reduced slack resources, making the effects of increased nurse staffing on reducing LOS and mortality ratios more readily discernible among these hospitals.

More details on the current study are in "The impact of HMO penetration on the relationship between nurse staffing and quality," by Dr. Mark, David W. Harless, Ph.D., and Michael McCue, D.B.A., in Health Economics, published online in March 2005 at

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