Annals of Emergency Medicine
Volume 49, Issue 3 , Pages 265-271, March 2007

Time Series Analysis of Variables Associated With Daily Mean Emergency Department Length of Stay

Presented at the American College of Emergency Physicians Research Forum, October 2004, San Francisco, CA.

  • Niels K. Rathlev, MD

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • Corresponding Author InformationAddress for correspondence: Niels K. Rathlev, MD, Department of Emergency Medicine, Boston Medical Center, One Boston Medical Center Place, Boston, MA 02118; 617-414-5963, fax 617-414-7759
    • ,
  • John Chessare, MD, MPH

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • ,
  • Jonathan Olshaker, MD

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • ,
  • Dan Obendorfer, MBA, MIS

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • ,
  • Supriya D. Mehta, PhD, MHS

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • ,
  • Todd Rothenhaus, MD

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • ,
  • Steven Crespo, MD

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • ,
  • Brendan Magauran, MD, MBA

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • ,
  • Kathy Davidson, MSN, MBA

      Affiliations

    • Nursing (Fisher, Guy), Senior Hospital Administration (Chessare, Davidson), Boston University Medical Center, Boston, MA
    • ,
  • Richard Shemin, MD

      Affiliations

    • Cardiothoracic Surgery (Shemin)
    • ,
  • Keith Lewis, MD

      Affiliations

    • Anesthesiology (Lewis)
    • ,
  • James M. Becker, MD

      Affiliations

    • Surgery (Becker)
    • ,
  • Linda Fisher, RN

      Affiliations

    • Departments of Emergency Medicine (Rathlev, Olshaker, Obendorfer, Mehta, Rothenhaus, Crespo, Magauran, Fisher)
    • Nursing (Fisher, Guy), Senior Hospital Administration (Chessare, Davidson), Boston University Medical Center, Boston, MA
    • ,
  • Linda Guy, RN

      Affiliations

    • Nursing (Fisher, Guy), Senior Hospital Administration (Chessare, Davidson), Boston University Medical Center, Boston, MA
    • ,
  • Abbott Cooper, MBA

      Affiliations

    • the Health Policy Institute, Boston University, Boston, MA (Cooper, Litvak)Drs. Chessare, Rothenhaus, and Crespo are currently affiliated with Caritas Christi Health Care System, Boston, MADr. Mehta is currently affiliated with the University of Illinois School of Public Health, Chicago, ILCooper is currently affiliated with Hospital Dynamics, Inc., Hampton, NH
    • ,
  • Eugene Litvak, PhD

      Affiliations

    • the Health Policy Institute, Boston University, Boston, MA (Cooper, Litvak)Drs. Chessare, Rothenhaus, and Crespo are currently affiliated with Caritas Christi Health Care System, Boston, MADr. Mehta is currently affiliated with the University of Illinois School of Public Health, Chicago, ILCooper is currently affiliated with Hospital Dynamics, Inc., Hampton, NH

Received in revised form 28 October 2005, 23 February 2006, 25 June 2006, 18 September 2006 and 13 October 2006; accepted 2 November 2006. published online 16 January 2007.

Study objective

We measure the effect of various input, throughput, and output factors on daily emergency department (ED) mean length of stay per patient (daily mean length of stay).

Methods

The study was a retrospective review of 93,274 ED visits between April 15, 2002, and December 31, 2003. The association between the daily mean length of stay and the independent variables was assessed with autoregressive moving average time series analysis (ARIMA). The following independent variables were measured per 24-hour period: number of elective surgical admissions, ED volume, number of ED admissions, number of ED ICU admissions, number of ED clinical attending hours, hospital medical-surgical occupancy (hospital occupancy), and day of the week.

Results

Three factors were independently associated with daily mean length of stay in time series analysis: number of elective surgical admissions, number of ED admissions, and hospital occupancy. The daily mean length of stay increased by 0.21 minutes for every additional elective surgical admission, 2.2 minutes for every additional admission, and 4.1 minutes for every 5% increase in hospital occupancy. Elective surgical admissions were associated with a maximum of 35 hours of additional ED dwell time. The model accounted for 31.5% of the variability in daily mean length of stay. The final model parameters for the ARIMA analysis were autoregressive term (1) moving average (1).

Conclusion

Hospital occupancy and the number of ED admissions are associated with daily mean length of stay. Every additional elective surgical admission prolonged the daily mean length of stay by 0.21 minutes per ED patient. Autocorrelation exists between the daily mean length of stay of the current day and the previous day.

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 Supervising editor: Brent R. Asplin, MD, MPH

 Author contributions: NKR, JC, JO, SDM, SC, BM, LF, and EL conceived the study and designed the trial. NKR, JC, JO, KD, and EL obtained the research funding. DO, SDM, TR, and AC provided statistical advice and analyzed the data. NKR, SC, BM, KD, RS, KL, JMB, LF, LG, and AC supervised the conduct of the trial and data collection. JC, DO, TR, RS, KL, JMB, and LG managed the data for analysis. All authors contributed substantively to the revision of the article. NKR drafted the article. NKR takes responsibility for the paper as a whole.

 Funding and support: This study was funded by the “Urgent Matters” Technical Assistance Grant (#048555) and Demonstration Grant (#048556) from the Robert Wood Johnson Foundation.

 Reprints not available from the authors.

PII: S0196-0644(06)02528-5

doi:10.1016/j.annemergmed.2006.11.007

Annals of Emergency Medicine
Volume 49, Issue 3 , Pages 265-271, March 2007

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