Background: Nursing studies have shown that nursing care delivery chan
ges affect staff and organizational outcomes, but the effects on clien
t outcomes have not been studied sufficiently. Objective: To describe,
at the level of the nursing care unit, the relationships among total
hours of nursing care, registered nurse (RN) skill mix, and adverse pa
tient outcomes. Methods: The adverse outcomes included unit rates of m
edication errors, patient falls, skin breakdown,patient and family com
plaints, infections, and deaths. The correlations among staffing varia
bles and outcome variables were determined, and multivariate analyses,
controlling for patient acuity, were completed.Results: Units with hi
gher average patient acuity had lower rates of medication errors and p
atient falls but higher rates of the other adverse outcomes. With aver
age patient acuity on the unit controlled, the proportion of hours of
care delivered by RNs was inversely related to the unit rates of medic
ation errors, decubiti, and patient complaints. Total hours of care fr
om all nursing personnel were associated directly with the rates of de
cubiti, complaints, and mortality. An unexpected finding was that the
relationship between RN proportion of care was curvilinear; as the RN
proportion increased, rates of adverse outcomes decreased up to 87.5%.
Above that level, as RN proportion increased, the adverse outcome rat
es also increased. Conclusions: The higher the RN skill mix, the lower
the incidence of adverse occurrences on inpatient care units.