| Needleman et al. (2002) [40] Cohort study Strong USA | Not reported | Administrative data from 1997 for 799 hospitals in 11 states, covering 5,075,969 discharges of medical patients and 1,104,659 surgical patients | A higher proportion of hours of care per day provided by registered nurses and a greater number of hours of care provided per day were associated with a shorter length of stay and lower rates of urinary tract infections and upper gastrointestinal bleeding. A higher hour of care provided by RNs was associated with a lower rate of pneumonia, shock or cardiac arrest, and “failure to rescue”. | Direct consequences: Patient harm |
| Person et al. (2004) [41] Cross-sectional analysis Moderate USA | Assess the association of nurse staffing with in-hospital mortality for patients with acute myocardial infarction. | 118,940 patients admitted with AMI in 6668 hospitals in the US | Patients treated in environments with higher RN staffing were less likely to die in-hospital. Patients treated in environments with higher LPN (licensed practical nurse) staffing were more likely to die in-hospital. (The data was adjusted with patient demographic, clinical characteristics, treatment, hospital volume, technology index teaching and urban status) | Direct consequences: Mortality |
| Potter et al. (2003) [54] Moderate Prospective, correlation study USA | To determine baseline values of patient outcome measures and the relationship of nurse staffing to patient outcomes. | 32 acute inpatient care units 3418 patients | The percentage of RN hours was negatively correlated with patient pain and self-care ability, and positive correlated with patient health status and five out of seven measures of post-discharge patient satisfaction. | Indirect consequences: Poor quality of basic care |
| Rogowski et al. (2013) [42] Retrospective cohort study Strong USA | To study the adequacy of Neo Natal Intensive Care Unit (NICU) nurse staffing in the United States using national guidelines and analyze its association with infant outcomes | newborn very low-birth-weight infants discharged from the NICUs in 2008 (n = 5771) and 2009 (n = 5630) All registered nurses with infant assignments. | The percentage of Very Low Birth Weight (VLBW) infants with hospital associated infections were 16.4% in 2008 and 13.9% in 2009. Relative to the guidelines, on average, hospitals understaffed 47% of all NICU infants in 2008 and 31% in 2009. A 1 standard deviation increase in the amount of a nurse per infant to meet the guidelines was associated with higher odds of infection in 2008 and 2009 | Direct consequences: Patient harm |
| Sasicbay-Akkadecbanunt et al. (2003) [43] cross-sectional study Moderate UK | To examine the association between in-hospital mortality and four nurse staffing variables. | Data of 2531 patients admitted to seven medical units and 10 surgical units of a 2300 bed university hospital. | The nurse-to-patient ratio was statistically correlated with in-hospital mortality. Nurse-to-patient ratio had an individual effect on in-hospital mortality. The ratio of total staff to patients was the best predictor of in hospital mortality among four staffing variables. There was not a significant relationship between in hospital mortality and the proportion of RNs to total nursing staff, the mean years of RN experience and the percentage of bachelor degree prepared nurses. | Direct consequences: Mortality |