Volume outcome relationship an econometric approach to cabg surgery
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Volume-Outcome Relationship: An Econometric Approach to CABG Surgery. Hsueh-Fen Chen (VCU) Gloria J. Bazzoli (VCU) Askar Chukmaitov (FSU) Funded by the Agency for Healthcare Research and Quality (HS 13094-03). Rationale for the Study.

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Volume outcome relationship an econometric approach to cabg surgery

Volume-Outcome Relationship: An Econometric Approach to CABG Surgery

Hsueh-Fen Chen (VCU)

Gloria J. Bazzoli (VCU)

Askar Chukmaitov (FSU)

Funded by the Agency for Healthcare Research and Quality (HS 13094-03)

Rationale for the study
Rationale for the Study Surgery

  • Clinicians and policymakers continue to debate the basis for volume-quality relationships:

    • Practice makes perfect

    • Selective referral

  • Outcomes of CABG surgery are of great interest:

    • one of the most common surgeries in the US

    • volume thresholds have been recommended by Leapfrog Group

    • regionalization vs non-regionalization

Research question
Research Question Surgery

  • Do volume-outcome relationships for CABG surgery in hospitals reflect selective referral, practice makes perfect, or both?

Findings from prior research
Findings from Prior Research Surgery

  • Several studies have found high CABG volume does not lead to better outcomes at the hospital level

    • (Luft, 1980; Luft, et al., 1987; Shroyer, 1996)

  • At patient level, mixed results exist about CABG volume-outcome relationship

    • (Hannan, et al., 1989; 1991; Shroyer, et al., 1996; Sollano et al., 1999; Birkmeyer, et al., 2002; Wu, et al., 2004; Peterson et al., 2004).

Limitations of prior research contribution of current study
Limitations of Prior Research: Contribution of Current Study Surgery

  • Is volume exogenous or endogenous?

  • Use of cross-sectional study design versus longitudinal study design

  • Generalizability of findings

Study methods and data sources
Study Methods and Data Sources Surgery

  • Research Approach

    • A longitudinal design: 1995 - 2000

  • Data Sources

    • HCUP-SID (AZ, CA, CO, FL, IA, MD, MA, NJ, NY, WA, WI)

    • AHA

    • ARF

    • InterStudy

  • Sample

    • 1,760 nonfederal, general short-term hospitals with at least 6 CABG surgeries a year

    • 1,200 of them had complete data

Analytical approach
Analytical Approach Surgery

  • The model for Practice Makes Perfect

    • Qualityit = β0+ β1 log( Volumeit )+ β2 Hospitalit + β3 Marketit + β4 IVQit+ β5 Statei + β6 Timeit + θi + εit

  • The model for Selective Referral

    • log(Volume)it = γ0 + γ1Qualityit + γ2 Hospitalit + γ3 Marketit + γ4 IVVit + γ5 Statei + γ6 Timeit + Ψi + μit

Measures Surgery

  • Primary Variables of Interest:

    • Quality: risk-adjusted in-hospital CABG mortality rate; calculated with AHRQ IQI software

    • Volume: log of the sum of discharges with the procedure ICD-9-CM codes: 3610-3619

  • Control Variables

    • Hospital Characteristics: ownership, teaching status, log (total surgical operations), system/ network affiliation, case-mixed adjusted length of stay

    • Market factors: log (per capita income) and HMO penetration at the MSA level

    • State and time dummy variables

Results of specification tests
Results of Specification Tests Surgery

  • Instruments are valid.

    • Instruments of volume (IVV): log (size), HHI, and tertiary services.

    • Instruments of quality (IVQ):

      • Staffing: RN and LPN per 1,000 inpatient days.

      • Severity of illness: patient acuity and case mix index.

  • Hospital-specific component of error exists (i.e., θi ≠0 and Ψi ≠0 ).

  • Fixed effects found to be preferred estimation method to random effects

Results Surgery

  • Practice makes perfect (DV: mortality)

  • Selective Referral (DV: log (volume))

Study limitations
Study Limitations Surgery

  • Administrative data used for constructing risk adjusted mortality rates

  • Strictly examine in-hospital mortality not mortality that occurs after discharge

  • Lack of data on physician volume

  • May be that practice makes perfect hypothesis is more relevant for physicians than for hospitals

Study implications
Study Implications Surgery

  • Longitudinal study design with instruments is recommended in future research on volume-quality relationships

  • From hospital perspective:

    • Regionalization of care based on volume thresholds may need to be reconsidered

    • Competition based on quality may be preferred.