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Overcoming bias in estimating the volume-outcome relationship
Alexander C Tsai1, Mark Votruba, John F P Bridges
1Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine WG-57, Cleveland, OH 44106-4945, USA.
Health Services Research
|January 25, 2006
Summary
Hospital volume does not significantly impact 30-day mortality for congestive heart failure (CHF) patients. Incorporating clinical data and advanced methods reveals that concentrating care in high-volume hospitals may not improve outcomes for elderly CHF patients.
Area of Science:
- Health Services Research
- Cardiology
- Health Economics
Background:
- Hospital volume is often presumed to correlate with patient outcomes.
- Previous studies on congestive heart failure (CHF) outcomes have primarily used administrative data.
- The impact of hospital volume on CHF patient mortality requires further investigation using comprehensive data.
Purpose of the Study:
- To evaluate the association between hospital volume and 30-day mortality in congestive heart failure (CHF) patients.
- To compare findings using conventional regression and instrumental variables (IV) estimation.
- To determine if clinical data significantly alter the perceived volume-outcome relationship.
Main Methods:
- Analysis of longitudinal data for 21,555 Medicare patients aged 65+ hospitalized for CHF (1991-1997).
- Utilized both administrative and clinical data for risk adjustment in linear probability models.
- Employed instrumental variables (IV) estimation using linear distances to address endogeneity of hospital volume.
Main Results:
- Initial analysis with administrative data showed a significant, but small, volume-outcome effect (p=.029).
- Adding clinical data attenuated the effect's magnitude and statistical significance (p=.39).
- Instrumental variables (IV) analysis indicated potential contamination from selective referral, but estimates remained consistent.
Conclusions:
- Relying solely on administrative data for volume-outcomes research may yield misleading results.
- Conventional estimates of the hospital volume-outcome relationship can be biased by patient selection.
- Current evidence does not support concentrating CHF care in high-volume hospitals to reduce elderly patient mortality.
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