Twigg et al.

(2011) [47]

Retrospective cohort study and

Time-series study



To determine the impact of implementing the NHPPD (Nursing hours per patient day) staffing method on 14 nursing-sensitive outcomes

236,453 patients from three adult hospital wards. Changes in nursing-sensitive outcomes were examined comparing the pre NHPPD-implementation-stage 0 and the post implementation-stage 2.

Significant decreases in the rates of nine out of fourteen nursing-sensitive outcomes when examining hospital-level data following implementation of NHPPD: Mortality, central nervous system complications, pressure ulcers, deep vein thrombosis, sepsis, ulcer/gastritis/upper gastrointestinal bleed, shock/cardiac arrest, pneumonia and average length of stay.

Direct consequences: Patient harm and patient mortality


(2003) [48]

Cohort study



To examine the changes in licensed nursing staff and assess the relationship of nursing staff with patient adverse events in hospitals

A convenience sample of all Pennsylvania, acute-care, hospitals, 1991 to 1997

Greater incidence of nearly all adverse events occurred in hospitals with fewer licensed nurses. There were a higher incidence of pressure ulcer and pneumonia in hospitals with a lower proportion of licensed nurses

Direct consequences: Patient harm

Van den Heedeet al.

(2009) [59]

Cross-sectional analysis



Examine the association between nurse staffing levels and 10 different patient outcomes potentially sensitive to nursing care

Data from 115 Belgian acute hospitals for the year 2003.

No significant relationship between acuity adjusted NHPPD (Nursing hours per patient day), proportions of registered nurses with at least a Bachelors’ degree and 10 patient outcomes.

No significant relationship

Weissman et al. (2007) [49]

Can’t tell



To determine the relationship between peak hospital workload and rates of adverse events.

A random sample of 24,676 patients discharged from the medical/surgical services at 4 US hospitals

Admissions and patients per nurse were significantly related to the likelihood of an adverse event. For example 0.1% increase in the patient-to-nurse ratio led to a 28% increase in the adverse event rate in one urban teaching hospital with high occupancy.

These results were only significant for this hospital. There were no significant results in the other three hospitals in the study.

Direct consequences patient harm

Yang (2003) [46]

Correlation study



To examine the effect of nurse staffing variables-daily average hours of care, ratio of RNs to average patients’ census, workload, and skill mix on patient outcomes as measured by five adverse occurrences

Data from hospital statistics. Sample composed of 347 FTE (fulltime equivalent) RNs distributed in 21 units with 793 beds ranging from 34 to 48 with a mean of 37.76 beds, as well as 29,424 inpatients.

Significantly positive correlation between daily average hours of care and urinary tract infections (r = 0.523, p < 0.05) and patient falls (r = 0.456, p < 0.05). Ratio of RNs to patient census negatively correlated to patient falls, urinary tract infections and complaints. Positive and significant relationship between workload and respiratory tract infections, patients’ complaints and their acuity level.

Direct consequences: Patient harm

Zhu et al.

(2012) [55]

Four stage sampling design



To examine the relationship between nurse staffing and patient outcomes in hospitals in mainland China.

7802 nurses and 5430 patients

Higher levels of nurses per patient had a statistically significant positive effect on the conduct of important nurse related tasks, and therefore on patient outcomes.

Indirect consequences: poor quality of basic care.