In this study of 30 hospital trusts in England, we found a large and consistent effect of nurse staffing on mortality outcomes in surgical patients as well as on nurse job outcomes and nurse ratings of quality of care. Hospitals in which nurses cared for the fewest patients each had significantly lower surgical mortality and FTR rates compared to those in which nurses cared for the greatest number of patients each. These findings are remarkably similar to those observed in 168 Pennsylvania hospitals studied at approximately the same time as part of the same international study (Aiken et al., 2002a
). In addition to an overall mortality rate of 2.3% in the patient population in the current study (the figure in Pennsylvania for a group of comparable patients was 2.0%), the contrasts between highest and lowest staffing levels revealed a decrease in mortality risk of 31% in Pennsylvania versus 26% in England. Thus, this study's results fit squarely into a rapidly expanding body of literature documenting a link between better nurse staffing and better patient outcomes. It is, to our knowledge, one of the first hospital outcomes studies based on UK patient and nurse data (Jarman et al., 1999
; UK Neonatal Staffing Study Group, 2002
), and the only one clearly linking better nurse staffing with lower mortality for common surgical procedures.
Using the final fully adjusted model and keeping all other characteristics of patients and hospitals constant, we used direct standardization procedures (Bishop et al., 1975
) to calculate that some 246 fewer deaths would have been seen in this subset of general surgery patients in 30 trusts had all been treated in hospitals with the most favourable staffing levels. Since our study involved only a sample of trusts and a subset of patients within those trusts, the number of lives that could potentially be saved through investments in nursing throughout NHS hospitals could be in the thousands every year. While this calculation incorporates a number of assumptions and must be interpreted with caution, it suggests the possible magnitude of the consequences of low staffing for the types of outcomes of greatest concern to policymakers and the public alike.
In addition to better outcomes for patients, hospitals with higher nurse staffing levels had significantly lower rates of nurse burnout and dissatisfaction. The nurses in the hospitals with the heaviest patient loads were 71% more likely to experience high burnout and job dissatisfaction than hospitals with the most favourable nurse staffing. Nurse burnout and dissatisfaction are precursors of nurse resignations (Sheward et al., 2005
; Lake, 1998
) and patient dissatisfaction (Vahey et al., 2004
). Our findings, like those of the US study (Aiken et al., 2002a
) suggest that better-staffed hospitals may be more successful in retaining their nurses. Hospitals and health systems internationally, as well as in the UK, are looking hard at maintaining and increasing the number of employed nurses to meet service and quality goals (Chancellor of the Exchequer, 2003
)—retention of currently employed nurses is key to meeting these goals.
Our findings that hospitals with more favourable nurse staffing show the best outcomes for patients and nurses provide the kind of research evidence called for by the UK Healthcare Commission in its report on ward staffing (Healthcare Commission, 2005
). The findings suggest that quality of care and nurse retention would improve if staffing levels across the NHS were brought more into line with those in the best-staffed hospitals in this study.
We have undertaken a number of tasks to verify the accuracy of our findings. The analyses were repeated in several different ways to ensure that the results reported here were robust to different cut-points for categorizing hospital workload levels to include and exclude slightly different groups of hospitals. Rates of poor outcomes for patients and nurses in hospitals in the lower (“better”) tertile on staffing were compared against those in hospitals in the upper two tertiles (a three-group categorization, introducing three more hospitals into the bottom and top groups) and in the lowest versus the other five quintiles (a five-group categorization taking one hospital out of those groups) were examined. The results were comparable to those in . Even more pronounced contrasts in outcomes were seen in trusts in the top and bottom fifths of hospitals on staffing. In addition to these sensitivity analyses, we confirmed that the results were robust to recalculating staffing statistics, restricting consideration to nurses from medical and surgical wards and excluding responses from a small number of nurses who reported very high patient loads (above 25 patients) on the last shift. Vascular patients, one of the diagnostic categories included among the general surgery patients studied, have higher risk for mortality than other general surgery patients. Thus, we tested the effects of staffing with and without including vascular patients and there were no differences.
Data were linked at the level of the hospital. While we were able to accurately classify nurses and patients into hospitals, we do not know to what extent the specific patients whose outcomes were studied here were cared for by the nurse respondents. The staffing statistics analysed were averages across shifts and specialties and while they are sound indicators of the availability of nursing time to patients across entire hospitals, they should not be interpreted as patient to nurse staffing ratios for implementation at the ward level.
The study has a number of strengths including carefully cleaned and validated hospital outcomes data, primary nurse survey data from a large sample of nurses in each study hospital, sound risk adjustment methods for the patient outcomes and appropriate controls for nurse and hospital characteristics. While measurement error and unmeasured differences in patient populations and hospital operations across acute hospitals may explain a portion of the effects seen here (as well as the lack of a consistent effect of staffing across hospitals in the middle range on staffing), we are confident that we have incorporated all of the relevant data available to us in this analysis.
In conclusion, this study is important in documenting that low levels of nurse staffing in UK hospitals have the same detrimental effects on patient outcomes and nurse retention that have been found in a large number of studies conducted primarily in North America. When considered alongside disturbing trends in the global nurse workforce (Buchan, 2002
) it suggests that problems with the supply of nurses and the possible impacts of variability in nurse staffing levels on patients cannot be considered solely N. American problems. To our knowledge this is the first UK study to document lower mortality and improved nurse retention in hospitals with more favourable patient nurse ratios. There is an urgent need for action by health system and hospital leaders internationally to implement strategies, which promote the retention and sustainability of the registered nurses in the workforce. Shortage is not just about numbers but also about how the health system functions to enable nurses to use their skills effectively.
What is already known about the topic?
- There is growing evidence from studies in the US that hospitals in which nurses care for fewer patients have better patient outcomes, but there is little evidence available internationally.
What this paper adds
- This large-scale national study of nurse staffing in the UK supports US findings that patients and nurses in hospitals with the most favourable staffing levels have better outcomes than those in less favourably staffed hospitals.
- Provides evidence that the positive relationship between low nurse: patient staffing ratios and favourable patient and nurse outcomes is an international phenomenon.