Development and Validation of a New Index to Measure Emergency Department Crowding

Abstract Objectives: To develop a quantitative measure of emergency department (ED) crowding and busyness. Methods: A five‐week study in spring 2002 in an urban teaching ED compared a new index (the Emergency Department Work Index EDWIN) with attending physician and nurse ratings of crowding. EDWIN is defined as ∑n it i/N a(B T−B A), where n i = number of patients in the ED in triage category i , t i = triage category, N a = number of attending physicians on duty, B T = number of treatment bays, and B A = number of admitted patients in the ED. The triage system used is the Emergency Severity Index (ESI), which was modified by reversing the ranking of triage categories; that is, an ESI score of 1 represented the least acute patient and 5 the sickest. EDWIN was calculated every two hours in a convenience sample of 60 eight‐hour shifts. With each measurement, the charge attending physician and nurse estimated how busy/crowded the ED was, using a Likert scale. Nurse and physician assessments were averaged and compared with EDWIN scores. Data were analyzed with SPSS 10.0 (SPSS Inc., Chicago, IL). Results: A total of 2,647 patients aged 18 years and older were assessed at 225 time points over 35 consecutive days. Nurses and physicians showed good interrater agreement of crowding assessment (weighted κ 0.61, 95% confidence interval = 0.53 to 0.69). Median EDWIN scores and interquartile ranges (IQRs) when the ED was rated as not busy, average, and very busy were 1.07 (IQR = 0.80 to 1.55), 1.55 (IQR = 1.16 to 1.93), and 1.83 (IQR = 1.42 to 2.45) (p < 0.001). The ED was on diversion for 17 time blocks (6.5% of all blocks), with a median EDWIN of 2.77 (IQR = 1.83 to 3.63), compared with an EDWIN of 1.45 (IQR = 1.05 to 2.00) when not on diversion (p < 0.001). EDWIN scores correlated weakly with various process‐of‐care measures chosen as secondary end points. Conclusions: EDWIN correlated well with staff assessment of ED crowding and diversion. The index can be programmed into tracking software for use as a “dashboard” to alert staff when the ED is approaching crisis. If validated across other sites, EDWIN may provide a tool to compare crowding levels among different EDs.