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The Very Real Effect That Questionable Statistical Analysis Has on Limiting Health Care Access for Bariatric Surgery

Edward H. Livingston, MD; Alan C. Elliott, MS; Linda S. Hynan, PhD; Eli Engel, MD, PhD

Arch Surg. 2007;142(10):979-987.

Hypothesis  Bariatric surgery for Medicare patients must be performed in an accredited hospital that performs at least 125 cases per year. We assessed the validity of this volume threshold and its policy implications.

Design  Using the 2001-2003 National Inpatient Survey, the effect of hospital volume on in-hospital mortality was statistically modeled and the effect of a 125–case per year threshold on access to bariatric surgery was calculated. We performed Monte Carlo modeling to investigate the effect random sampling has on the apparently high mortality rate for low-volume hospitals.

Setting  US inpatient hospitals.

Patients  Patients with hospital discharge codes indicating bariatric surgery.

Main Outcome Measure  In-house mortality.

Results  The observed in-hospital mortality distribution as a function of hospital volume was similar to the expected frequency attributable to random sampling alone. A small number of excess deaths in very low-volume facilities cause statistically significant results for volume-outcome studies. Although 74% of all bariatric surgeries are performed in high-volume centers, 73% of all hospitals currently offering these services are now classified as low volume.

Conclusions  When the results of statistical analysis are used for policy determination, the consequences for patient care may be substantial. Most studies of volume-outcome relationships rely on statistical methods that tend to amplify the effects and few fully characterize their statistical models. Despite the weak evidence for a volume-outcome relationship for bariatric surgery, a 125–case per year threshold has been set for center-of-excellence status, which eliminates most hospitals currently providing these services and disproportionately restricts access for the poor and underinsured.

Author Affiliations: Divisions of Gastrointestinal and Endocrine Surgery (Dr Livingston) and Biostatistics (Drs Elliott and Hynan), University of Texas Southwestern School of Medicine and the Veterans Administration North Texas Health Care System, Dallas; and the Department of Biomathematics, University of California, Los Angeles (Dr Engel).