| Schreuders et al. (2014) [57] Retrospective longitudinal study Moderate Australia | To compare characteristics of hospitalizations with and without complications and examine the impact of nurse staffing on inpatient complications | Administrative data from Western Australian Department of Health (2001-2008) | Nurse staffing levels were not associated with decreased patient complication risks. | No significant relationship |
| Seynaeve et al. (2011) [56] Cross-sectional survey. Moderate USA, Antwerp | 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. | 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 |
| Shuldham et al. (2008) [58] Retrospective case control study Strong UK | To explore the relationship between nurse staffing characteristics and patient outcomes. | All patients, included day cases, who were admitted at two hospitals as an in-patient over 12 months | Weak association between nurse staffing and the majority of the outcomes in the lower dependency category wards. The Incidence Rate Ratio (IRR) for falls, GI bleeds, sepsis and Deep Vein Thrombosis (DVT) were reduced where nursing hour per patient day increased, but the numbers were not statistical significant. When adding bank hours (extra staff from the hospital), in addition to the permanent staff, only the result of pressure sores and DVT reached statistical significance. | No statistical significance. Indirect consequences: Patient harm |
| Stone et al. (2007) [44] Observational study Moderate USA | To examine effects of a comprehensive set of working condition on elderly patient safety outcome in intensive care units. | To examine effects of a comprehensive set of working condition on elderly patient safety outcome in intensive care units. | Units with higher staffing levels had lower incidence of CLBSI (central line blood stream infections), ventilator-associated pneumonia, 30-day mortality and pressure ulcer. | Direct consequences: Patient harm. |
| Tarnow-Mordi et al. (2000) [45] Retrospective observational analyses Strong UK | Not reported | 1050 admissions in the ICU | Adjusted mortality were more than two times higher in patients exposed to low ICU workload. After exclusion of measures of nursing requirement, adjusted mortality increased with the ratio of occupied to appropriately staffed beds during each patient’s stay. | Direct consequence: Mortality |