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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
Measures
  • 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
  • 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
Results
  • Practice makes perfect (DV: mortality)
  • Selective Referral (DV: log (volume))
study limitations
Study Limitations
  • 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
  • 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.
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