• Melissa L McCarthy, Scott L Zeger, Ru Ding, Scott R Levin, Jeffrey S Desmond, Jennifer Lee, and Dominik Aronsky.
• Department of Emergency Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21209, USA. mmccarth@jhmi.edu
• Ann Emerg Med. 2009 Oct 1;54(4):492-503.e4.

Study ObjectiveWe determine the effect of crowding on emergency department (ED) waiting room, treatment, and boarding times across multiple sites and acuity groups.MethodsThis was a retrospective cohort study that included ED visit and inpatient medicine occupancy data for a 1-year period at 4 EDs. We measured crowding at 30-minute intervals throughout each patient's ED stay. We estimated the effect of crowding on waiting room time, treatment time, and boarding time separately, using discrete-time survival analysis with time-dependent crowding measures (ie, number waiting, number being treated, number boarding, and inpatient medicine occupancy rate), controlling for patient demographic and clinical characteristics.ResultsCrowding substantially delayed patients' waiting room and boarding times but not treatment time. During the day shift, when the number boarding increased from the 50th to the 90th percentile, the adjusted median waiting room time (range 26 to 70 minutes) increased by 6% to 78% (range 33 to 82 minutes), and the adjusted median boarding time (range 250 to 626 minutes) increased by 15% to 47% (range 288 to 921 minutes), depending on the site. Crowding delayed the care of high-acuity level 2 patients at all sites. During crowded periods (ie, 90%), the adjusted median waiting room times of high-acuity level 2 patients were 3% to 35% higher than during normal periods, depending on the site and crowding measure.ConclusionUsing discrete-time survival analysis, we were able to dynamically measure crowding throughout each patient's ED visit and demonstrate its deleterious effect on the timeliness of emergency care, even for high-acuity patients.

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