Table 1: A comparison of crowding scales.

Crowding ScaleCalculationOutcomeNotes

Real-time emergency analysis of demand Indicators scores (READI) [35]     DV > 7 indicates overcrowding, and further assessment is recommended.The acuity ratio is based on a four-level acuity scale (4 being most acute).
A BR > 1 indicates overcrowding.Poor agreement between READI score and staff perception of crowding [36].
A PR > 1.5 indicates an understaffed ED.
AR close to 1 indicates a low burden of illness: AR close to 4 indicates a severe burden of illness.
Demand value (DV) provides an overall measure of demand based on current calculations of the three ratios.
Bed ratio (BR) assesses the demand per treatment space.
Provider ratio (PR) calculates how many patients can be seen by the physician providers based on the average number of patients seen per hour
(PPH) by each physician.
Acuity ratio (AR) measures the relative burden of illness by averaging the triage categories of all patients in the ED.

Emergency department work index (EDWIN) [37]
The number of patients present in the ED in triage category .
The triage category (ordinal scale 1–5, 5 being most acute).
The number of attending physicians on duty at a given time.
The total number of beds, or treatment bays, available in the ED.
The number of admitted patients (boarders) in the ED.
EDWIN score < 1.5
Active but manageable ED
EDWIN score 1.5–2.0
A busy ED has an
EDWIN score > 2
A crowded ED
The triage system used was an inverted emergency severity index (ESI).
The scale was initially evaluated against nurse/physician perception of crowding.
Has been shown to be a strong predictor of ambulance diversion and to correlate well with staff perception of crowding [38].

Emergency department crowding scoreExact calculations for the EDCS are unclear, however, the specific inputs to the EDCS are the following:
(i) number of attending emergency physicians,
(ii) number of staffed ED beds,
(iii) number of critical care patients,
(iv) number of total ED patients,
(v) number of staffed hospital beds,
(vi) hospital occupancy rate.
EDCS score > 65 was found to be predictive of both ambulance diversion and the number of patients who leave without being seen by a physician.Generates an output score between 0 and 100.
Three variables were identified that independently predicted physician and nurse ratings of EDC: (1) the number of boarders, (2) the total number of ED patients, and (3) the number of critical care ED patients.

National emergency department overcrowding study (NEDOCS) [26] 0–50: normal
51–100: busy
101–140: overcrowded
141–180: severe
>180: disaster
Generates an output score between 0 and 200 however higher scores are possible.
Weiss has demonstrated that NEDOCS is highly correlated with clinicians’ perceptions of crowding, ambulance diversion, and patients leaving without being seen [39]

Total Patients Total number of patients in the ED, including those in the waiting room, fast track
or observation areas.
ED Beds Total number of ED beds, including those in hallways, fast track areas, chairs,
and elsewhere.
Admits Total number of boarders/admitted patients in the ED at the time the score is
calculated.
Hospital Beds Total number of hospital beds, typically the number of licensed beds that could
be used in a disaster.
Ventilators The number of patients in the ED on ventilators or respirators
Longest Admit The longest patient boarding time (in hours) at which the score is calculated
Last Bed Time The time (in hours) from arrival to bed for the last patient assigned to a bed.

ED work Score [40] Using the threshold work score = 4.77, predict the decision for ambulance diversion with 86% sensitivity and 80% specificity.Published in 2006 by Epstein and Tian
Developed to be used in real time to direct ambulance traffic based on an objective measure of ED status.
The triage system used was an inverted emergency severity index (ESI).
Sometimes referred to as the Boston ED workscore.

Number of patients in the waiting room.
The total number of beds, or treatment bays, available in the ED.
The number of patients present in the ED in triage category .
The triage category (ordinal scale 1–5, 5 being most acute).
Number of nurses on duty.
The number of admitted patients (boarders) in the ED.

ED occupancy Rate ED occupancy rate above 1.0 indicates there are more ED patients than treatment bays.
The threshold to indicate crowding differs from study to study. Examples are OR = 1.0, 1.2, and 1.4.
Suggested to be the simplest and overall best indicator of crowding. [13, 41]

Total patients (number of patients in the ED including those in the waiting room, boarding, hallway, and chairs.)
BT (the total number of licensed treatment bays including fast track or observation units, excluding hallway locations.)