Varied definitions of hospital volume did not alter the conclusions of volume-outcome analyses.
OBJECTIVE
To compare different methods of calculating hospital volume, including approaches designed to account for hospital restructuring, and their impact on volume-outcome analyses.


METHODS
Using a population-based cohort of acute myocardial infarction (AMI) patients hospitalized between 1992 and 2004 in Ontario, Canada, we assessed the association between hospital volume and 30-day mortality using four different volume definitions. Bootstrapping was used to compare the odds ratios (ORs) of the different volume definitions.


RESULTS
All four of the volume definitions tested resulted in statistically significant volume-outcome analyses. Using external data to account for hospital restructuring did not alter the conclusions of volume-outcome analyses. Nevertheless, statistically significant heterogeneity in the magnitude of the estimated ORs for the volume-outcome relationship was observed across the different volume measurement methods.


CONCLUSIONS
The conclusions of hospital volume-outcome analyses are similar regardless of how hospital volume is defined. However, the heterogeneity in the volume ORs suggests that direct policy application of these ORs requires the most accurate method of defining volume.
Kulkarni
Girish S
GS
Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada.
Laupacis
Andreas
A
Urbach
David R
DR
Fleshner
Neil E
NE
Austin
Peter C
PC
D006276:Health Facility Size / Q000706:statistics & numerical data*; D017052:Hospital Mortality; D006801:Humans; D009203:Myocardial Infarction / Q000401:mortality / Q000628:therapy*; D016017:Odds Ratio; D009864:Ontario; D017063:Outcome Assessment, Health Care; D011379:Prognosis