title: Crowding measures associated with the quality of emergency department care: a systematic review.
abstract: OBJECTIVE
  Despite the substantial body of literature on emergency department (ED) crowding, to the best of our knowledge, there is no agreement on the measure or measures that should be used to quantify crowding. The objective of this systematic review was to identify existing measures of ED crowding that have been linked to quality of care as defined by the Institute of Medicine (IOM) quality domains (safe, effective, patient-centered, efficient, timely, and equitable).
  
  
  METHODS
  Six major bibliographic databases were searched from January 1980 to January 2012, and hand searches were conducted of relevant journals and conference proceedings. Observational studies (cross-sectional, cohort, and case-control), quality improvement studies, quasi-experimental (e.g., before/after) studies, and randomized controlled trials were considered for inclusion. Studies that did not provide measures of ED crowding were excluded. Studies that did not provide quantitative data on the link between crowding measures and quality of care were also excluded. Two independent reviewers assessed study eligibility, completed data extraction, and assessed study quality using the Newcastle-Ottawa Quality Assessment Scale (NOS) for observational studies and a modified version of the NOS for cross-sectional studies.
  
  
  RESULTS
  The search identified 7,413 articles. Thirty-two articles were included in the review: six cross-sectional, one case-control, 23 cohort, and two retrospective reviews of performance improvement data. Methodologic quality was moderate, with weaknesses in the reporting of study design and methodology. Overall, 15 of the crowding measures studied had quantifiable links to quality of care. The three measures most frequently linked to quality of care were the number of patients in the waiting room, ED occupancy (percentage of overall ED beds filled), and the number of admitted patients in the ED awaiting inpatient beds. None of the articles provided data on the link between crowding measures and the IOM domains reflecting equitable and efficient care.
  
  
  CONCLUSIONS
  The results of this review provide data on the association between ED crowding measures and quality of care. Three simple crowding measures have been linked to quality of care in multiple publications.
authors.affiliation: Division of Emergency Medicine, Alberta Children's Hospital, Alberta Children's Hospital Research Institute, Department of Pediatrics and Community Health Sciences, University of Calgary, Calgary, Alberta.
authors.forename: Antonia S
authors.initials: AS
authors.lastname: Stang
authors.affiliation: Division of Emergency Medicine, Alberta Children's Hospital, Department of Pediatrics, University of Calgary, Calgary, Alberta.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Crotts
authors.affiliation: Division of Emergency Medicine, Alberta Children's Hospital, Alberta Children's Hospital Research Institute, Department of Pediatrics, Physiology and Pharmacology, University of Calgary, Calgary, Alberta.
authors.forename: David W
authors.initials: DW
authors.lastname: Johnson
authors.affiliation: Department of Pediatrics, University of Alberta, Alberta Research Center for Health Evidence, Edmonton, Alberta.
authors.forename: Lisa
authors.initials: L
authors.lastname: Hartling
authors.affiliation: Division of Pediatric Medicine, Hospital for Sick Children, Department of Pediatrics and Health Policy, Management and Evaluation, University of Toronto and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada.
authors.forename: Astrid
authors.initials: A
authors.lastname: Guttmann
mesh_terms: D003441:Crowding; D004632:Emergency Medical Services; D004636:Emergency Service, Hospital / Q000458:organization & administration* / Q000592:standards; D005260:Female; D006801:Humans; D008297:Male; D010343:Patient Admission; D019984:Quality Indicators, Health Care; D011787:Quality of Health Care / Q000458:organization & administration*; D014481:United States; D014850:Waiting Lists