Skip to content
View commentaries on this research

Please note that this summary was posted more than 5 years ago. More recent research findings may have been published.

This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Higher registered nurse staffing levels are associated with lower mortality, and the fact that fewer vital sign observations are missed is the most likely explanation for this. Increasing registered nursing staff by an hour for each patient per day could reduce the risk of death by 3%.

If the ratio of healthcare assistants to nurses gets too high, the data also suggest that rates of missed vital sign observations and mortality increase in line with the extra registered nurse time spent supervising other staff.

Increases in nursing skill mix, by having proportionately more registered nurses, may be cost-effective for improving patient safety.

This NIHR-funded observational study in a large hospital was carefully designed to address an important question about staffing levels and the potential explanations for variations in care in a complex system. As such, the findings will be useful for informing how hospital and ward managers think about the appropriate staffing levels for their services and the approach to take across different types of ward.

Why was this study needed?

A high ratio of patients to nurses in hospital contributes to poor patient care and increased patient mortality. The number of acute admissions has increased by 21% over the past decade, while the number of nurses caring for adults in hospitals increased by just 8%.

In June 2018, there were 41,000 full-time NHS vacancies for nurses in England. In the context of chronic short staffing, it is important to know which nursing activities and skill mix show the greatest improvement in patients’ outcomes. A systematic review found that planning and communication activities were reported as missed more often than clinical care when nursing staff levels were low.

This research aimed to address one of the research gaps identified in NICE safe staffing guidance from 2014.

What did this study do?

This observational study assessed how staffing levels were linked to patients’ care across 32 adult medical and surgical wards in one hospital in southern England over three years.

The number of nurses, healthcare assistants and temporary staff on duty and vital sign observations for 138,133 patients were measured using the hospital’s computerised records. Observations delayed by more than two-thirds of the scheduled interval were classed as ‘missed’.

Statistical modelling estimated the effects on patients of changes in staff levels compared with normal levels. The statistical models considered the route of admission and the patient’s severity of illness.

The observational design of this study means that it is not possible to conclude that, on their own, staffing levels or vital signs observations caused changes in patients’ outcomes.

What did it find?

  • For each day that the registered nurses staffing level was below the average for that ward, the risk of death during the first five days of admission increased by 3% (hazard ratio [HR] 1.03, 95% confidence interval [CI] 1.01 to 1.06). Similarly, the risk increased by 4% for each day that the healthcare assistant staffing level was below average (HR 1.04, 95% CI 1.02 to 1.07).
  • Each additional hour worked by registered nurses per patient each day reduced the risk of death by 3% (HR 0.97, 95% CI 0.94 to 1.00). A higher number of hours worked by registered nurses per patient each day was associated with fewer missed observations in sicker patients (incidence rate ratio [IRR] 0.98, 95% CI 0.98 to 0.99).
  • No effect on risk of death was seen for additional healthcare assistant hours worked per patient each day (HR 1.01, 95% CI 0.98 to 1.04)­ but a higher number of hours worked by healthcare assistants per patient each day was associated with fewer missed observations (IRR 0.95, 95% CI 0.95 to 0.96).
  • When more than 1.5 temporary staff hours were worked per patient each day, the risk of death increased by 12% (HR 1.12, 95% CI 1.03 to 1.21).
  • The statistical model suggested that if there were a 0.32 increase in registered nurse staffing levels and similar decrease in healthcare assistants (so that the skill mix was in line with that planned by the Trust) this could reduce the death rate by 2%. It could avoid 50 deaths per year and prevent 4,464 bed-days. Though staff costs would increase by £28 per patient, overall costs would decrease due to fewer bed-days.

What does current guidance say on this issue?

The 2014 NICE guideline on safe staffing for nursing of adults in acute hospitals noted that no single staff-to-patient ratio could be applied across all acute adult inpatient wards.

The 2018 improvement resource for safe, sustainable and productive staffing from the National Quality Board built on recommendations from NICE. It recommends using a systematic approach to staffing levels, informed by an evidence-based decision-support tool, professional judgement and peer-comparison.

Flexible working policies and efficient deployment of staff should be used to limit the use of temporary staff.

What are the implications?

This study is consistent with previous evidence of increased mortality with fewer registered nurses. It adds further evidence that missed vital sign observations may be one factor that could explain how lower nursing staff levels affect patients’ outcomes. However, the relationship between all the possible factors is complex.

The finding of worse mortality with higher numbers of temporary staff is consistent with recommendations from the National Quality Board to limit the use of temporary staff. How to achieve increased levels of clinical time while there are large numbers of registered nurse vacancies in the NHS remains a challenge, and this study adds to other research that helps hospital managers better understand the difficult issue.

Citation and Funding

Griffiths P, Ball J, Bloor K et al. Nurse staffing levels, missed vital signs and mortality in hospitals: retrospective longitudinal observational study. Health Serv Deliv Res. 2018;6(38).

This project was funded by the NIHR Health Services and Delivery Research Programme (project number 13/114/17).



CQC. 2017 Adult inpatient survey. Statistical release. London. Care Quality Commission; 2018.

CQC The state of health care and adult social care in England 2017/18. London. Care Quality Commission; 2018.

Griffiths P, Recio-Saucedo A, Dall'Ora C et al. The association between nurse staffing and omissions in nursing care: a systematic review. J Adv Nurs. 2018;74(4):1474-87.

National Quality Board. Safe, sustainable and productive staffing. An improvement resource for adult inpatient wards in acute hospitals. London. NHS England; 2018.

NICE. Safe staffing for nursing in adult inpatient wards in acute hospitals. SG1. London: National Institute for Health and Care Excellence; 2014.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


  • Share via:
  • Print article
Back to top