Nurse staffing, nursing assistants and hospital mortality: retrospective longitudinal observational study

Peter Griffiths, Antonello Maruotti, Alejandra Recio-Saucedo, Oliver Redfern, Jane Ball, Jim Briggs, Chiara Dall'Ora, Paul E. Schmidt, Gary B. Smith

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Objectives - To determine the association between daily levels of registered nurse (RN) and nursing assistant staffing and hospital mortality. 

Setting - 32 general wards in a NHS general hospital in England. 

Design - Retrospective longitudinal observational study using routinely collected data. We used multilevel/hierarchical mixed-effects regression models to explore the association between patient outcomes and daily variation in RN and nursing assistant staffing, measured as hours per patient per day relative to ward mean. Analyses were controlled for ward, and patient risk. 

Participants - 138,133 adult patients spending >1 days on general wards between 1 April 2012 and 31 March 2015. 

Outcomes - In-hospital deaths. 

Results - Hospital mortality was 4.1%. The hazard of death was increased by 3% for every day a patient experienced RN staffing below ward mean (adjusted hazard ratio [aHR; 95% CI] = 1.03; 1.01-1.05). Relative to ward mean, each additional hour of RN care available over the first five days of a patient’s stay was associated with 3% reduction in the hazard of death (aHR 0.97; 0.94-1.0). Days where admissions per RN exceeded 125% of the ward mean were associated with an increased hazard of death (aHR 1.05; 1.01-1.09). Although low nursing assistant staffing was associated with increases in mortality, high nursing assistant staffing was also associated with increased mortality. 

Conclusions - Lower RN staffing and higher levels of admissions per RN are associated with increased risk of death during an admission to hospital. These findings highlight the possible consequences of reduced nurse staffing, and do not give support to policies that encourage the use of nursing assistants to compensate for shortages of RNs.
Original languageEnglish
Pages (from-to)609-617
JournalBMJ Quality and Safety
Early online date4 Dec 2018
Publication statusEarly online - 4 Dec 2018


  • Hospital Units/ manpower
  • Hospital Mortality
  • Retrospective Studies
  • Length of stay
  • Hospital/supply & distribution
  • Nursing Staff


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