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Minimum nurse-to-patient ratios cut mortality risk by up to 11% — Australia study

Research examining the effect of minimum nurse-to-patient ratios has found it reduces the risks of those in care dying by up to 11%. The study, published in The Lancet, also found that length of stay fell by 9% and that there were fewer readmissions.

The research team from the University of Pennsylvania School of Nursing examined two years of data, based on nurses in direct contact with patients on medical wards. They compared the odds of dying within 30 days of admission and the odds of being readmitted within seven days of discharge.

In 2016, 27 hospitals in Queensland were required to adopt minimum nurse to patient ratios while 28 others did not. The state has a policy of just one nurse to every four patients during the day and one to seven at night, in a bid to improve safety and standards of care. It compared 400,000 patients and 17,000 nurses working in those 27 hospitals to the 28 other hospitals.

Lead author, professor Matthew McHugh said: “Our findings plug a crucial data gap that has delayed a widespread roll-out of nurse staffing mandates. Opponents of these policies often raise concerns that there is no clear evaluation of policy, so we hope that our data convinces people of the need for minimum nurse-to-patient ratios by clearly demonstrating that quality nursing is vital to patient safety and care.”

But the study did not fully compare like for like hospitals and only 30 per cent of nurses responded to the study surveys, reports The Independent. The level of staffing at the hospitals improved by an average of only half a patient per nurse and were better staffed than comparison hospitals to begin with. arm, to the measures of positive contribution to health, wellbeing and satisfaction.”

Professor Peter Griffiths from the University of Southampton, who worked on the UK National Institute for Health and Care Excellence (NICE) safe staffing project, told The Independent: “When we reviewed the research for NICE in 2014, the evidence that nurse staffing levels influenced important outcomes for hospital patients, including the risk of death, seemed compelling. However, the direct evidence that policies such as mandatory minimum ratios was very limited. Such limitation has often been cited as a reason for not supporting specific recommendations in policy.

“This new study is the first large scale prospective study of the costs and effects of implementing a mandatory minimum policy. It shows that implementing a mandatory minimum of one nurse to four patients was linked to a reduction in deaths and potentially cost savings through shorter stays and avoided readmissions.”

He added: “It is striking that staffing levels in a lot of UK hospitals are far lower than this. It is important to remember that, based on the evidence of this and other studies, staffing shortfalls would need to be filled by registered nurses. Current policies in some areas, England in particular, involve creating new grades of staff below the registered nurse, where there is no evidence for benefit. I also note that many in the UK call for mandatory minimums but it is really important that the staffing level that is mandated is right. Having a minimum that is too low is also dangerous.”

The Royal College of Nursing said the study added to the existing evidence on how crucial nurses were to safety. Pat Cullen, chief executive said: “Every time the nurse number drops, mortality increases – that's how critical we are to safe patient care.

“There are tens of thousands of unfilled nurse jobs right now. Patients cannot afford for the government to keep ducking this issue. Accountability for workforce planning must be included in the forthcoming legislation for NHS and care services in England.”

The Independent writes that NHS England has resisted moves towards minimum nurse to patient ratios, suspended work by the National Institute for Health and Care Excellence (NICE) on safe nurse staffing in 2015. This came as the watchdog was preparing to call for minimum ratios in accident and emergency departments. NICE has said that eight or more patients to one nurse on a general ward is the point at which harm can start to occur to patients.

During the Coronavirus pandemic staffing ratios in intensive care, which are normally one to one, were suspended in the NHS with some nurses stretched to look after up to four patients. Other hospitals left ward nurses looking after 16 or more patients.

Dr Elaine Maxwell, a former chief nurse and author of a review of staffing evidence for the National Institute for Health Research, said: “I'm not persuaded this study adds anything to our knowledge. The original Magnet study was important as it demonstrated a link, but it is now time to look at context and variation to avoid simplifying a complex situation in an unhelpful way. I'd also like to see a move away from negative definitions of nursing as only preventing harm, to the measures of positive contribution to health, wellbeing and satisfaction.”

Study details

Effects of nurse-to-patient ratio legislation on nurse staffing and patient mortality, readmissions, and length of stay: a prospective study in a panel of hospitals

Authors:Matthew D McHughLinda H AikenDouglas M SloaneCarol WindsorClint DouglasPatsy Yates

Published: May 11, 2021 in The Lancet



Substantial evidence indicates that patient outcomes are more favourable in hospitals with better nurse staffing. One policy designed to achieve better staffing is minimum nurse-to-patient ratio mandates, but such policies have rarely been implemented or evaluated. In 2016, Queensland (Australia) implemented minimum nurse-to-patient ratios in selected hospitals. We aimed to assess the effects of this policy on staffing levels and patient outcomes and whether both were associated.


For this prospective panel study, we compared Queensland hospitals subject to the ratio policy (27 intervention hospitals) and those that discharged similar patients but were not subject to ratios (28 comparison hospitals) at two timepoints: before implementation of ratios (baseline) and 2 years after implementation (post-implementation). We used standardised Queensland Hospital Admitted Patient Data, linked with death records, to obtain data on patient characteristics and outcomes (30-day mortality, 7-day readmissions, and length of stay [LOS]) for medical-surgical patients and survey data from 17 010 medical-surgical nurses in the study hospitals before and after policy implementation. Survey data from nurses were used to measure nurse staffing and, after linking with standardised patient data, to estimate the differential change in outcomes between patients in intervention and comparison hospitals, and determine whether nurse staffing changes were related to it.


We included 231 902 patients (142 986 in intervention hospitals and 88 916 in comparison hospitals) assessed at baseline (2016) and 257 253 patients (160 167 in intervention hospitals and 97 086 in comparison hospitals) assessed in the post-implementation period (2018). After implementation, mortality rates were not significantly higher than at baseline in comparison hospitals (adjusted odds ratio [OR] 1·07, 95% CI 0·97–1·17, p=0·18), but were significantly lower than at baseline in intervention hospitals (0·89, 0·84–0·95, p=0·0003). From baseline to post-implementation, readmissions increased in comparison hospitals (1·06, 1·01–1·12, p=0·015), but not in intervention hospitals (1·00, 0·95–1·04, p=0·92). Although LOS decreased in both groups post-implementation, the reduction was more pronounced in intervention hospitals than in comparison hospitals (adjusted incident rate ratio [IRR] 0·95, 95% CI 0·92–0·99, p=0·010). Staffing changed in hospitals from baseline to post-implementation: of the 36 hospitals with reliable staffing measures, 30 (83%) had more than 4·5 patients per nurse at baseline, with the number decreasing to 21 (58%) post-implementation. The majority of change was at intervention hospitals, and staffing improvements by one patient per nurse produced reductions in mortality (OR 0·93, 95% CI 0·86–0·99, p=0·045), readmissions (0·93, 0·89–0·97, p<0·0001), and LOS (IRR 0·97, 0·94–0·99, p=0·035). In addition to producing better outcomes, the costs avoided due to fewer readmissions and shorter LOS were more than twice the cost of the additional nurse staffing.


Minimum nurse-to-patient ratio policies are a feasible approach to improve nurse staffing and patient outcomes with good return on investment.


Full The Lancet study (Open access)


Full The Independent report (Open access)


See also from the MedicalBrief archives:


Nursing shortage is compromising SA healthcare


Poor nursing means rehospitalisation

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