An evidence-based approach to safe staffing

Research consistently confirms that safe nurse staffing is critical to quality of care and patient safety.

An aging population, advances in technology and declining lengths of stay have steadily increased patient acuity in hospitals. Nursing care requires continuous patient assessment, critical thinking and expert judgement. When staffing levels are too low, RNs are often forced to compromise the care they give to their patients.

Unsafe nurse staffing is a dangerous practice that leads to medical errors, poorer patient outcomes and nursing injuries as well as burnout.

Key findings from research studies on safe nurse staffing

Patient mortality risk increases by 7% for each additional patient added to a nurse’s workload

Aiken et al., conducted a large cross-sectional analysis of linked data from 10,184 staff nurse surveys, 232,342 surgical patients who were discharged, and administrative data from 168 hospitals to estimate the probability of failure to rescue (deaths within 30 days of admission in patients who experienced complications) and mortality (death) risk for each patient under various patient-to-nurse ratios (i.e., 4,6, & 8 patients per nurse).

This study demonstrated a significant 7% increased mortality risk for every surgical patient added to the average nurse-patient workload. The mortality risk jumped to 14% when a nurse’s patient load went from 4-6 and a 31% mortality risk when that load went from 6-8 patients.

This study clearly illustrates the benefit of adequate staffing and direct correlation with safe patient outcomes.

Aiken, L. H., Clarke, S. P., Sloane, D. M., Sochalski, J., & Silber, J. H. (2002). Hospital nurse staffing and patient mortality, nurse burnout, and job dissatisfaction. JAMA, 288(16), 1987-1993.


Enhanced nursing work environments, staffing and higher levels of nursing education positively impact risk of patient mortality

A large observational study examined the effects of nurse staffing, work environment and nurse education on patient mortality in 14 high-tech teaching hospitals with at least 700 beds. This study linked facility data from each hospital to nurse survey data from 1,024 nurses and discharge data from 76,036 surgical patients.

This study demonstrated a 5% increased risk of mortality with each additional patient per nurse, a 50% decrease in mortality risk in hospitals with good versus mixed/poor nurse environments and a 9% decrease in mortality risk with 10% increase in staff nurses who had a bachelor’s degree in nursing.

Patient outcomes and risk for mortality are linked to a constellation of key variables.

Cho, E., Sloane, D. M., Kim, E. Y., Kim, S., Choi, M., Yoo, I. Y., . . . Aiken, L. H. (2015). Effects of nurse staffing, work environments, and education on patient mortality: an observational study. Int J Nurs Stud, 52(2), 535-542. doi:10.1016/j.ijnurstu.2014.08.006


Adequate nurse staffing and higher education decrease chances of patient mortality

A cross-sectional data analysis, looking for patient mortality directly associated with missed nursing care and nurse staffing levels, was performed. Combined data from date range 2009-2011 was collected on 422,730 surgical patients and from 26,516 registered nurses, in 300 general acute hospitals across nine countries.

These results showed that for each additional patient per nurse increase, a patient has a 7% increased risk of dying within 30 days of admission and for every 10% increase in missed nursing care (due to lack of time) there was a 16% increased risk of a patient dying within 30 days.

These are dismal statistics, but this study was able to demonstrate that these findings can be mediated when nurse staffing levels are adequate and nurses are more highly educated; for every 10% increase in bachelor’s degree nurses there was a 7% decreased likelihood of dying.

Ball, J. E., Bruyneel, L., Aiken, L. H., Sermeus, W., Sloane, D. M., Rafferty, A. M., . . . Consortium, R. N. C. (2018). Post-operative mortality, missed care and nurse staffing in nine countries: A cross-sectional study. Int J Nurs Stud, 78, 10-15. doi:10.1016/j.ijnurstu.2017.08.004


Patient activity and acuity have a direct impact on work demands of nurses and are independent risk factors for patient mortality

Needleman and colleagues performed a large cross-sectional study that examined the association between nurse staffing levels and patient mortality.

This study retrospectively analyzed data from 197,961 hospital admissions and 176, 696 nursing shifts that were 8 hours in length across 43 hospital units in a tertiary care medical center. The study monitored several other variables that could be associated with patient mortality including units with high shift turnover where there were volumes of admissions, transfers and discharges that would increase the demands of the nurses.

The results revealed a positive correlation with patient’s mortality risk where there are high turnover units and nurse staffing well below the target levels and reinforces the critical importance in matching staffing with patients’ needs for nursing care.

Needleman, J., Buerhaus, P., Pankratz, V. S., Leibson, C. L., Stevens, S. R., & Harris, M. (2011). Nurse staffing and inpatient hospital mortality. N Engl J Med, 364(11), 1037-1045. doi:10.1056/NEJMsa1001025



For a comprehensive list of research, see the American Nurses Association’s Safe Staffing Literature Review.