Objective Getting staffing levels wrong in hospitals is linked to excess mortality and poor patient experiences but establishing the safe nurse staffing levels in the emergency department (ED) is challenging because patient demand is so variable. This paper reports a review conducted for the National Institute for Health and Care Excellence (NICE) which sought to identify the research evidence to inform UK nursing workforce planning.

Design We searched 10 electronic databases and relevant websites for English language studies published from 1994. Studies included reported a direct measure of nurse staffing relative to an activity measure (eg, attendances, patient throughput) or an estimate of nurse staffing requirements. Randomised or non-randomised trials, prospective or retrospective observational, cross-sectional or correlational studies, interrupted time-series, and controlled before and after studies were considered.

Results We identified 16 132 items via databases and 2193 items through manual and other searching. After title/abstract screening (by one reviewer, checked by a second) 55 studies underwent full assessment by the review team. 18 studies met the inclusion criteria for the NICE review, however 3 simulation studies that reported simulated rather than measured outcomes are not reported here.

Conclusions The evidence is weak but indicates that levels of nurse staffing in the ED are associated with patients leaving without being seen, ED care time and patient satisfaction. Lower staffing is associated with worse outcomes. There remain significant gaps and in particular a lack of evidence on the impact of staffing on direct patient outcomes and adequate economic analyses to inform decisions about nurse staffing. Given that an association between nurse staffing levels and patient outcomes on inpatient wards has been demonstrated, this gap in the evidence about nurse staffing in EDs needs to be addressed.