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Higher staffing levels linked to reduced risk of inpatient death

Posted on 10/02/2016

A study led by King’s College London and the University of Southampton has shown that a higher registered nurse to patient ratio is linked to a reduced risk of inpatient death.

The study of staffing levels in NHS hospitals, published in the online journal BMJ Open, found that in trusts where registered nurses had six or fewer patients to care for, the death rate for patients with medical conditions was 20 per cent lower than in those where they had more than 10. Hospitals with more doctors per bed also had lower death rates but hospitals with more unregistered nursing support workers may have had higher death rates.

The study, by researchers from King’s College London, the University of Southampton, Karolinska Institutet, Stockholm and the New York School of Medicine, analysed two measures over two years (2009-11: the number of beds per registered nurse, doctor, and healthcare support worker in 137 acute care trusts; and the number of patients per ward nurse, drawn from a survey of just under 3000 registered nurses in a nationally representative sample of 31 of these trusts (46 hospitals and 401 wards).

They also calculated the predicted number of deaths for medical and surgical inpatients, taking account of influential factors, such as age, other underlying conditions, and number of emergency admissions during the previous 12 months.

Among patients admitted to medical, wards, higher death rates were associated with higher numbers of occupied beds for each registered nurse and for each doctor employed by the trust. By contrast, higher numbers of healthcare support workers were associated with higher rates of inpatient death.

When all staff groups were included in the statistical analysis of all 137 trusts, the associations remained significant only for doctors and healthcare support workers.

But analysis focussing on nurses actually working on wards of the subsidiary group of 31 trusts showed that the death rate was 20 per cent lower in those where each registered nurse cared for an average of six or fewer medical inpatients than in trusts were each registered nurse cared for 10 or more. These associations remained significant after further statistical analysis.

The results on surgical wards were similar, with higher registered nurse to patient ratios associated with a 17 per cent lower inpatient death rate.

The registered nurse headcount varied by as much as a factor of four between those at the top and bottom of the staffing scale. Even after taking account of all nursing staff, this variation only dropped to a threefold difference between those with the highest and lowest nurse headcounts.

This is an observational study, so no firm conclusions can be drawn about cause and effect, added to which the findings on nurse to patient ratios are based on only 31 trusts.

Previous research suggests that the nurse to patient ratio has an association with outcomes such as mortality, but few studies have taken account of the impact of other members of clinical staff.

There is still not enough evidence on which to base firm recommendations on specific safe staffing levels in the UK, but policies geared towards substituting registered nurses with healthcare support workers (healthcare assistants and auxiliary nurses) should at the very least be reviewed, conclude the researchers.

Anne Marie Rafferty, Professor of Nursing Policy, King’s College London, says: “This is the first study to shed light on the policy of shifting the safe staffing policy decision from nursing to that of the clinical team. It flags the need for caution and the dangers of simply substituting healthcare support staff for qualified nursing staff”.   

Professor Peter Griffiths, Chair of Health Services Research at the University of Southampton, NIHR CLAHRC (Wessex), comments: “This does not, in itself, provide a robust basis to identify safe staffing thresholds but given the overall strength of evidence for an association, we are showing that, in England, the registered nursing workforce is clearly associated with patient safety. And we found no evidence that having more support workers is associated with reduced death rates in hospital. Some of our findings suggest the opposite. A policy of replacing registered nurses with support staff may threaten patient safety.”

Jane Ball, Principal Research Fellow NIHR CLAHRC (Wessex), adds: “When determining the safety of nurse staffing on hospital wards, the level of registered nurse staffing is crucial; hospitals with higher levels of healthcare support workers have higher mortality rates.

“Patients should not be asked to pay the price  of receiving care from a less skilled and less educated member of staff,  just to make up for the failure of the system to ensure  enough registered nurses. Staffing decisions need to be made on the basis of patient safety, not on the basis of finance. Current policies geared towards substituting [these] workers for registered nurses should be reviewed.”


For further information, please contact Hannah Siddall, Senior Communications Officer, on 020 7848 3062 or at 

Notes for editors:

  1. Research: Registered nurse, healthcare support worker, medical staffing levels and mortality in English hospital trusts: a cross-sectional study doi 10.1136/bmjopen-2015-008751
  2. The National Institute for Health Research (NIHR) is funded by the Department of Health to improve the health and wealth of the nation through research. Since its establishment in April 2006, the NIHR has transformed research in the NHS. It has increased the volume of applied health research for the benefit of patients and the public, driven faster translation of basic science discoveries into tangible benefits for patients and the economy, and developed and supported the people who conduct and contribute to applied health research. The NIHR plays a key role in the Government’s strategy for economic growth, attracting investment by the life-sciences industries through its world-class infrastructure for health research. Together, the NIHR people, programmes, centres of excellence and systems represent the most integrated health research system in the world. For further information, visit the NIHR website (
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